2 * INET An implementation of the TCP/IP protocol suite for the LINUX
3 * operating system. INET is implemented using the BSD Socket
4 * interface as the means of communication with the user level.
6 * Implementation of the Transmission Control Protocol(TCP).
9 * Fred N. van Kempen, <waltje@uWalt.NL.Mugnet.ORG>
10 * Mark Evans, <evansmp@uhura.aston.ac.uk>
11 * Corey Minyard <wf-rch!minyard@relay.EU.net>
12 * Florian La Roche, <flla@stud.uni-sb.de>
13 * Charles Hedrick, <hedrick@klinzhai.rutgers.edu>
14 * Linus Torvalds, <torvalds@cs.helsinki.fi>
15 * Alan Cox, <gw4pts@gw4pts.ampr.org>
16 * Matthew Dillon, <dillon@apollo.west.oic.com>
17 * Arnt Gulbrandsen, <agulbra@nvg.unit.no>
18 * Jorge Cwik, <jorge@laser.satlink.net>
22 * Changes: Pedro Roque : Retransmit queue handled by TCP.
23 * : Fragmentation on mtu decrease
24 * : Segment collapse on retransmit
27 * Linus Torvalds : send_delayed_ack
28 * David S. Miller : Charge memory using the right skb
29 * during syn/ack processing.
30 * David S. Miller : Output engine completely rewritten.
31 * Andrea Arcangeli: SYNACK carry ts_recent in tsecr.
32 * Cacophonix Gaul : draft-minshall-nagle-01
33 * J Hadi Salim : ECN support
39 #include <linux/compiler.h>
40 #include <linux/gfp.h>
41 #include <linux/module.h>
43 /* People can turn this off for buggy TCP's found in printers etc. */
44 int sysctl_tcp_retrans_collapse __read_mostly = 1;
46 /* People can turn this on to work with those rare, broken TCPs that
47 * interpret the window field as a signed quantity.
49 int sysctl_tcp_workaround_signed_windows __read_mostly = 0;
51 /* This limits the percentage of the congestion window which we
52 * will allow a single TSO frame to consume. Building TSO frames
53 * which are too large can cause TCP streams to be bursty.
55 int sysctl_tcp_tso_win_divisor __read_mostly = 3;
57 int sysctl_tcp_mtu_probing __read_mostly = 0;
58 int sysctl_tcp_base_mss __read_mostly = TCP_BASE_MSS;
60 /* By default, RFC2861 behavior. */
61 int sysctl_tcp_slow_start_after_idle __read_mostly = 1;
63 int sysctl_tcp_cookie_size __read_mostly = 0; /* TCP_COOKIE_MAX */
64 EXPORT_SYMBOL_GPL(sysctl_tcp_cookie_size);
67 /* Account for new data that has been sent to the network. */
68 static void tcp_event_new_data_sent(struct sock *sk, const struct sk_buff *skb)
70 struct tcp_sock *tp = tcp_sk(sk);
71 unsigned int prior_packets = tp->packets_out;
73 tcp_advance_send_head(sk, skb);
74 tp->snd_nxt = TCP_SKB_CB(skb)->end_seq;
76 /* Don't override Nagle indefinitely with F-RTO */
77 if (tp->frto_counter == 2)
80 tp->packets_out += tcp_skb_pcount(skb);
81 if (!prior_packets || tp->early_retrans_delayed)
85 /* SND.NXT, if window was not shrunk.
86 * If window has been shrunk, what should we make? It is not clear at all.
87 * Using SND.UNA we will fail to open window, SND.NXT is out of window. :-(
88 * Anything in between SND.UNA...SND.UNA+SND.WND also can be already
89 * invalid. OK, let's make this for now:
91 static inline __u32 tcp_acceptable_seq(const struct sock *sk)
93 const struct tcp_sock *tp = tcp_sk(sk);
95 if (!before(tcp_wnd_end(tp), tp->snd_nxt))
98 return tcp_wnd_end(tp);
101 /* Calculate mss to advertise in SYN segment.
102 * RFC1122, RFC1063, draft-ietf-tcpimpl-pmtud-01 state that:
104 * 1. It is independent of path mtu.
105 * 2. Ideally, it is maximal possible segment size i.e. 65535-40.
106 * 3. For IPv4 it is reasonable to calculate it from maximal MTU of
107 * attached devices, because some buggy hosts are confused by
109 * 4. We do not make 3, we advertise MSS, calculated from first
110 * hop device mtu, but allow to raise it to ip_rt_min_advmss.
111 * This may be overridden via information stored in routing table.
112 * 5. Value 65535 for MSS is valid in IPv6 and means "as large as possible,
113 * probably even Jumbo".
115 static __u16 tcp_advertise_mss(struct sock *sk)
117 struct tcp_sock *tp = tcp_sk(sk);
118 const struct dst_entry *dst = __sk_dst_get(sk);
119 int mss = tp->advmss;
122 unsigned int metric = dst_metric_advmss(dst);
133 /* RFC2861. Reset CWND after idle period longer RTO to "restart window".
134 * This is the first part of cwnd validation mechanism. */
135 static void tcp_cwnd_restart(struct sock *sk, const struct dst_entry *dst)
137 struct tcp_sock *tp = tcp_sk(sk);
138 s32 delta = tcp_time_stamp - tp->lsndtime;
139 u32 restart_cwnd = tcp_init_cwnd(tp, dst);
140 u32 cwnd = tp->snd_cwnd;
142 tcp_ca_event(sk, CA_EVENT_CWND_RESTART);
144 tp->snd_ssthresh = tcp_current_ssthresh(sk);
145 restart_cwnd = min(restart_cwnd, cwnd);
147 while ((delta -= inet_csk(sk)->icsk_rto) > 0 && cwnd > restart_cwnd)
149 tp->snd_cwnd = max(cwnd, restart_cwnd);
150 tp->snd_cwnd_stamp = tcp_time_stamp;
151 tp->snd_cwnd_used = 0;
154 /* Congestion state accounting after a packet has been sent. */
155 static void tcp_event_data_sent(struct tcp_sock *tp,
158 struct inet_connection_sock *icsk = inet_csk(sk);
159 const u32 now = tcp_time_stamp;
161 if (sysctl_tcp_slow_start_after_idle &&
162 (!tp->packets_out && (s32)(now - tp->lsndtime) > icsk->icsk_rto))
163 tcp_cwnd_restart(sk, __sk_dst_get(sk));
167 /* If it is a reply for ato after last received
168 * packet, enter pingpong mode.
170 if ((u32)(now - icsk->icsk_ack.lrcvtime) < icsk->icsk_ack.ato)
171 icsk->icsk_ack.pingpong = 1;
174 /* Account for an ACK we sent. */
175 static inline void tcp_event_ack_sent(struct sock *sk, unsigned int pkts)
177 tcp_dec_quickack_mode(sk, pkts);
178 inet_csk_clear_xmit_timer(sk, ICSK_TIME_DACK);
181 /* Determine a window scaling and initial window to offer.
182 * Based on the assumption that the given amount of space
183 * will be offered. Store the results in the tp structure.
184 * NOTE: for smooth operation initial space offering should
185 * be a multiple of mss if possible. We assume here that mss >= 1.
186 * This MUST be enforced by all callers.
188 void tcp_select_initial_window(int __space, __u32 mss,
189 __u32 *rcv_wnd, __u32 *window_clamp,
190 int wscale_ok, __u8 *rcv_wscale,
193 unsigned int space = (__space < 0 ? 0 : __space);
195 /* If no clamp set the clamp to the max possible scaled window */
196 if (*window_clamp == 0)
197 (*window_clamp) = (65535 << 14);
198 space = min(*window_clamp, space);
200 /* Quantize space offering to a multiple of mss if possible. */
202 space = (space / mss) * mss;
204 /* NOTE: offering an initial window larger than 32767
205 * will break some buggy TCP stacks. If the admin tells us
206 * it is likely we could be speaking with such a buggy stack
207 * we will truncate our initial window offering to 32K-1
208 * unless the remote has sent us a window scaling option,
209 * which we interpret as a sign the remote TCP is not
210 * misinterpreting the window field as a signed quantity.
212 if (sysctl_tcp_workaround_signed_windows)
213 (*rcv_wnd) = min(space, MAX_TCP_WINDOW);
219 /* Set window scaling on max possible window
220 * See RFC1323 for an explanation of the limit to 14
222 space = max_t(u32, sysctl_tcp_rmem[2], sysctl_rmem_max);
223 space = min_t(u32, space, *window_clamp);
224 while (space > 65535 && (*rcv_wscale) < 14) {
230 /* Set initial window to a value enough for senders starting with
231 * initial congestion window of TCP_DEFAULT_INIT_RCVWND. Place
232 * a limit on the initial window when mss is larger than 1460.
234 if (mss > (1 << *rcv_wscale)) {
235 int init_cwnd = TCP_DEFAULT_INIT_RCVWND;
238 max_t(u32, (1460 * TCP_DEFAULT_INIT_RCVWND) / mss, 2);
239 /* when initializing use the value from init_rcv_wnd
240 * rather than the default from above
243 *rcv_wnd = min(*rcv_wnd, init_rcv_wnd * mss);
245 *rcv_wnd = min(*rcv_wnd, init_cwnd * mss);
248 /* Set the clamp no higher than max representable value */
249 (*window_clamp) = min(65535U << (*rcv_wscale), *window_clamp);
251 EXPORT_SYMBOL(tcp_select_initial_window);
253 /* Chose a new window to advertise, update state in tcp_sock for the
254 * socket, and return result with RFC1323 scaling applied. The return
255 * value can be stuffed directly into th->window for an outgoing
258 static u16 tcp_select_window(struct sock *sk)
260 struct tcp_sock *tp = tcp_sk(sk);
261 u32 cur_win = tcp_receive_window(tp);
262 u32 new_win = __tcp_select_window(sk);
264 /* Never shrink the offered window */
265 if (new_win < cur_win) {
266 /* Danger Will Robinson!
267 * Don't update rcv_wup/rcv_wnd here or else
268 * we will not be able to advertise a zero
269 * window in time. --DaveM
271 * Relax Will Robinson.
273 new_win = ALIGN(cur_win, 1 << tp->rx_opt.rcv_wscale);
275 tp->rcv_wnd = new_win;
276 tp->rcv_wup = tp->rcv_nxt;
278 /* Make sure we do not exceed the maximum possible
281 if (!tp->rx_opt.rcv_wscale && sysctl_tcp_workaround_signed_windows)
282 new_win = min(new_win, MAX_TCP_WINDOW);
284 new_win = min(new_win, (65535U << tp->rx_opt.rcv_wscale));
286 /* RFC1323 scaling applied */
287 new_win >>= tp->rx_opt.rcv_wscale;
289 /* If we advertise zero window, disable fast path. */
296 /* Packet ECN state for a SYN-ACK */
297 static inline void TCP_ECN_send_synack(const struct tcp_sock *tp, struct sk_buff *skb)
299 TCP_SKB_CB(skb)->tcp_flags &= ~TCPHDR_CWR;
300 if (!(tp->ecn_flags & TCP_ECN_OK))
301 TCP_SKB_CB(skb)->tcp_flags &= ~TCPHDR_ECE;
304 /* Packet ECN state for a SYN. */
305 static inline void TCP_ECN_send_syn(struct sock *sk, struct sk_buff *skb)
307 struct tcp_sock *tp = tcp_sk(sk);
310 if (sysctl_tcp_ecn == 1) {
311 TCP_SKB_CB(skb)->tcp_flags |= TCPHDR_ECE | TCPHDR_CWR;
312 tp->ecn_flags = TCP_ECN_OK;
316 static __inline__ void
317 TCP_ECN_make_synack(const struct request_sock *req, struct tcphdr *th)
319 if (inet_rsk(req)->ecn_ok)
323 /* Set up ECN state for a packet on a ESTABLISHED socket that is about to
326 static inline void TCP_ECN_send(struct sock *sk, struct sk_buff *skb,
329 struct tcp_sock *tp = tcp_sk(sk);
331 if (tp->ecn_flags & TCP_ECN_OK) {
332 /* Not-retransmitted data segment: set ECT and inject CWR. */
333 if (skb->len != tcp_header_len &&
334 !before(TCP_SKB_CB(skb)->seq, tp->snd_nxt)) {
336 if (tp->ecn_flags & TCP_ECN_QUEUE_CWR) {
337 tp->ecn_flags &= ~TCP_ECN_QUEUE_CWR;
338 tcp_hdr(skb)->cwr = 1;
339 skb_shinfo(skb)->gso_type |= SKB_GSO_TCP_ECN;
342 /* ACK or retransmitted segment: clear ECT|CE */
343 INET_ECN_dontxmit(sk);
345 if (tp->ecn_flags & TCP_ECN_DEMAND_CWR)
346 tcp_hdr(skb)->ece = 1;
350 /* Constructs common control bits of non-data skb. If SYN/FIN is present,
351 * auto increment end seqno.
353 static void tcp_init_nondata_skb(struct sk_buff *skb, u32 seq, u8 flags)
355 skb->ip_summed = CHECKSUM_PARTIAL;
358 TCP_SKB_CB(skb)->tcp_flags = flags;
359 TCP_SKB_CB(skb)->sacked = 0;
361 skb_shinfo(skb)->gso_segs = 1;
362 skb_shinfo(skb)->gso_size = 0;
363 skb_shinfo(skb)->gso_type = 0;
365 TCP_SKB_CB(skb)->seq = seq;
366 if (flags & (TCPHDR_SYN | TCPHDR_FIN))
368 TCP_SKB_CB(skb)->end_seq = seq;
371 static inline int tcp_urg_mode(const struct tcp_sock *tp)
373 return tp->snd_una != tp->snd_up;
376 #define OPTION_SACK_ADVERTISE (1 << 0)
377 #define OPTION_TS (1 << 1)
378 #define OPTION_MD5 (1 << 2)
379 #define OPTION_WSCALE (1 << 3)
380 #define OPTION_COOKIE_EXTENSION (1 << 4)
382 struct tcp_out_options {
383 u8 options; /* bit field of OPTION_* */
384 u8 ws; /* window scale, 0 to disable */
385 u8 num_sack_blocks; /* number of SACK blocks to include */
386 u8 hash_size; /* bytes in hash_location */
387 u16 mss; /* 0 to disable */
388 __u32 tsval, tsecr; /* need to include OPTION_TS */
389 __u8 *hash_location; /* temporary pointer, overloaded */
392 /* The sysctl int routines are generic, so check consistency here.
394 static u8 tcp_cookie_size_check(u8 desired)
399 /* previously specified */
402 cookie_size = ACCESS_ONCE(sysctl_tcp_cookie_size);
403 if (cookie_size <= 0)
404 /* no default specified */
407 if (cookie_size <= TCP_COOKIE_MIN)
408 /* value too small, specify minimum */
409 return TCP_COOKIE_MIN;
411 if (cookie_size >= TCP_COOKIE_MAX)
412 /* value too large, specify maximum */
413 return TCP_COOKIE_MAX;
416 /* 8-bit multiple, illegal, fix it */
419 return (u8)cookie_size;
422 /* Write previously computed TCP options to the packet.
424 * Beware: Something in the Internet is very sensitive to the ordering of
425 * TCP options, we learned this through the hard way, so be careful here.
426 * Luckily we can at least blame others for their non-compliance but from
427 * inter-operatibility perspective it seems that we're somewhat stuck with
428 * the ordering which we have been using if we want to keep working with
429 * those broken things (not that it currently hurts anybody as there isn't
430 * particular reason why the ordering would need to be changed).
432 * At least SACK_PERM as the first option is known to lead to a disaster
433 * (but it may well be that other scenarios fail similarly).
435 static void tcp_options_write(__be32 *ptr, struct tcp_sock *tp,
436 struct tcp_out_options *opts)
438 u8 options = opts->options; /* mungable copy */
440 /* Having both authentication and cookies for security is redundant,
441 * and there's certainly not enough room. Instead, the cookie-less
442 * extension variant is proposed.
444 * Consider the pessimal case with authentication. The options
446 * COOKIE|MD5(20) + MSS(4) + SACK|TS(12) + WSCALE(4) == 40
448 if (unlikely(OPTION_MD5 & options)) {
449 if (unlikely(OPTION_COOKIE_EXTENSION & options)) {
450 *ptr++ = htonl((TCPOPT_COOKIE << 24) |
451 (TCPOLEN_COOKIE_BASE << 16) |
452 (TCPOPT_MD5SIG << 8) |
455 *ptr++ = htonl((TCPOPT_NOP << 24) |
457 (TCPOPT_MD5SIG << 8) |
460 options &= ~OPTION_COOKIE_EXTENSION;
461 /* overload cookie hash location */
462 opts->hash_location = (__u8 *)ptr;
466 if (unlikely(opts->mss)) {
467 *ptr++ = htonl((TCPOPT_MSS << 24) |
468 (TCPOLEN_MSS << 16) |
472 if (likely(OPTION_TS & options)) {
473 if (unlikely(OPTION_SACK_ADVERTISE & options)) {
474 *ptr++ = htonl((TCPOPT_SACK_PERM << 24) |
475 (TCPOLEN_SACK_PERM << 16) |
476 (TCPOPT_TIMESTAMP << 8) |
478 options &= ~OPTION_SACK_ADVERTISE;
480 *ptr++ = htonl((TCPOPT_NOP << 24) |
482 (TCPOPT_TIMESTAMP << 8) |
485 *ptr++ = htonl(opts->tsval);
486 *ptr++ = htonl(opts->tsecr);
489 /* Specification requires after timestamp, so do it now.
491 * Consider the pessimal case without authentication. The options
493 * MSS(4) + SACK|TS(12) + COOKIE(20) + WSCALE(4) == 40
495 if (unlikely(OPTION_COOKIE_EXTENSION & options)) {
496 __u8 *cookie_copy = opts->hash_location;
497 u8 cookie_size = opts->hash_size;
499 /* 8-bit multiple handled in tcp_cookie_size_check() above,
502 if (0x2 & cookie_size) {
503 __u8 *p = (__u8 *)ptr;
505 /* 16-bit multiple */
506 *p++ = TCPOPT_COOKIE;
507 *p++ = TCPOLEN_COOKIE_BASE + cookie_size;
508 *p++ = *cookie_copy++;
509 *p++ = *cookie_copy++;
513 /* 32-bit multiple */
514 *ptr++ = htonl(((TCPOPT_NOP << 24) |
516 (TCPOPT_COOKIE << 8) |
517 TCPOLEN_COOKIE_BASE) +
521 if (cookie_size > 0) {
522 memcpy(ptr, cookie_copy, cookie_size);
523 ptr += (cookie_size / 4);
527 if (unlikely(OPTION_SACK_ADVERTISE & options)) {
528 *ptr++ = htonl((TCPOPT_NOP << 24) |
530 (TCPOPT_SACK_PERM << 8) |
534 if (unlikely(OPTION_WSCALE & options)) {
535 *ptr++ = htonl((TCPOPT_NOP << 24) |
536 (TCPOPT_WINDOW << 16) |
537 (TCPOLEN_WINDOW << 8) |
541 if (unlikely(opts->num_sack_blocks)) {
542 struct tcp_sack_block *sp = tp->rx_opt.dsack ?
543 tp->duplicate_sack : tp->selective_acks;
546 *ptr++ = htonl((TCPOPT_NOP << 24) |
549 (TCPOLEN_SACK_BASE + (opts->num_sack_blocks *
550 TCPOLEN_SACK_PERBLOCK)));
552 for (this_sack = 0; this_sack < opts->num_sack_blocks;
554 *ptr++ = htonl(sp[this_sack].start_seq);
555 *ptr++ = htonl(sp[this_sack].end_seq);
558 tp->rx_opt.dsack = 0;
562 /* Compute TCP options for SYN packets. This is not the final
563 * network wire format yet.
565 static unsigned int tcp_syn_options(struct sock *sk, struct sk_buff *skb,
566 struct tcp_out_options *opts,
567 struct tcp_md5sig_key **md5)
569 struct tcp_sock *tp = tcp_sk(sk);
570 struct tcp_cookie_values *cvp = tp->cookie_values;
571 unsigned int remaining = MAX_TCP_OPTION_SPACE;
572 u8 cookie_size = (!tp->rx_opt.cookie_out_never && cvp != NULL) ?
573 tcp_cookie_size_check(cvp->cookie_desired) :
576 #ifdef CONFIG_TCP_MD5SIG
577 *md5 = tp->af_specific->md5_lookup(sk, sk);
579 opts->options |= OPTION_MD5;
580 remaining -= TCPOLEN_MD5SIG_ALIGNED;
586 /* We always get an MSS option. The option bytes which will be seen in
587 * normal data packets should timestamps be used, must be in the MSS
588 * advertised. But we subtract them from tp->mss_cache so that
589 * calculations in tcp_sendmsg are simpler etc. So account for this
590 * fact here if necessary. If we don't do this correctly, as a
591 * receiver we won't recognize data packets as being full sized when we
592 * should, and thus we won't abide by the delayed ACK rules correctly.
593 * SACKs don't matter, we never delay an ACK when we have any of those
595 opts->mss = tcp_advertise_mss(sk);
596 remaining -= TCPOLEN_MSS_ALIGNED;
598 if (likely(sysctl_tcp_timestamps && *md5 == NULL)) {
599 opts->options |= OPTION_TS;
600 opts->tsval = TCP_SKB_CB(skb)->when;
601 opts->tsecr = tp->rx_opt.ts_recent;
602 remaining -= TCPOLEN_TSTAMP_ALIGNED;
604 if (likely(sysctl_tcp_window_scaling)) {
605 opts->ws = tp->rx_opt.rcv_wscale;
606 opts->options |= OPTION_WSCALE;
607 remaining -= TCPOLEN_WSCALE_ALIGNED;
609 if (likely(sysctl_tcp_sack)) {
610 opts->options |= OPTION_SACK_ADVERTISE;
611 if (unlikely(!(OPTION_TS & opts->options)))
612 remaining -= TCPOLEN_SACKPERM_ALIGNED;
615 /* Note that timestamps are required by the specification.
617 * Odd numbers of bytes are prohibited by the specification, ensuring
618 * that the cookie is 16-bit aligned, and the resulting cookie pair is
622 (OPTION_TS & opts->options) &&
624 int need = TCPOLEN_COOKIE_BASE + cookie_size;
627 /* 32-bit multiple */
628 need += 2; /* NOPs */
630 if (need > remaining) {
631 /* try shrinking cookie to fit */
636 while (need > remaining && TCP_COOKIE_MIN <= cookie_size) {
640 if (TCP_COOKIE_MIN <= cookie_size) {
641 opts->options |= OPTION_COOKIE_EXTENSION;
642 opts->hash_location = (__u8 *)&cvp->cookie_pair[0];
643 opts->hash_size = cookie_size;
645 /* Remember for future incarnations. */
646 cvp->cookie_desired = cookie_size;
648 if (cvp->cookie_desired != cvp->cookie_pair_size) {
649 /* Currently use random bytes as a nonce,
650 * assuming these are completely unpredictable
651 * by hostile users of the same system.
653 get_random_bytes(&cvp->cookie_pair[0],
655 cvp->cookie_pair_size = cookie_size;
661 return MAX_TCP_OPTION_SPACE - remaining;
664 /* Set up TCP options for SYN-ACKs. */
665 static unsigned int tcp_synack_options(struct sock *sk,
666 struct request_sock *req,
667 unsigned int mss, struct sk_buff *skb,
668 struct tcp_out_options *opts,
669 struct tcp_md5sig_key **md5,
670 struct tcp_extend_values *xvp)
672 struct inet_request_sock *ireq = inet_rsk(req);
673 unsigned int remaining = MAX_TCP_OPTION_SPACE;
674 u8 cookie_plus = (xvp != NULL && !xvp->cookie_out_never) ?
678 #ifdef CONFIG_TCP_MD5SIG
679 *md5 = tcp_rsk(req)->af_specific->md5_lookup(sk, req);
681 opts->options |= OPTION_MD5;
682 remaining -= TCPOLEN_MD5SIG_ALIGNED;
684 /* We can't fit any SACK blocks in a packet with MD5 + TS
685 * options. There was discussion about disabling SACK
686 * rather than TS in order to fit in better with old,
687 * buggy kernels, but that was deemed to be unnecessary.
689 ireq->tstamp_ok &= !ireq->sack_ok;
695 /* We always send an MSS option. */
697 remaining -= TCPOLEN_MSS_ALIGNED;
699 if (likely(ireq->wscale_ok)) {
700 opts->ws = ireq->rcv_wscale;
701 opts->options |= OPTION_WSCALE;
702 remaining -= TCPOLEN_WSCALE_ALIGNED;
704 if (likely(ireq->tstamp_ok)) {
705 opts->options |= OPTION_TS;
706 opts->tsval = TCP_SKB_CB(skb)->when;
707 opts->tsecr = req->ts_recent;
708 remaining -= TCPOLEN_TSTAMP_ALIGNED;
710 if (likely(ireq->sack_ok)) {
711 opts->options |= OPTION_SACK_ADVERTISE;
712 if (unlikely(!ireq->tstamp_ok))
713 remaining -= TCPOLEN_SACKPERM_ALIGNED;
716 /* Similar rationale to tcp_syn_options() applies here, too.
717 * If the <SYN> options fit, the same options should fit now!
721 cookie_plus > TCPOLEN_COOKIE_BASE) {
722 int need = cookie_plus; /* has TCPOLEN_COOKIE_BASE */
725 /* 32-bit multiple */
726 need += 2; /* NOPs */
728 if (need <= remaining) {
729 opts->options |= OPTION_COOKIE_EXTENSION;
730 opts->hash_size = cookie_plus - TCPOLEN_COOKIE_BASE;
733 /* There's no error return, so flag it. */
734 xvp->cookie_out_never = 1; /* true */
738 return MAX_TCP_OPTION_SPACE - remaining;
741 /* Compute TCP options for ESTABLISHED sockets. This is not the
742 * final wire format yet.
744 static unsigned int tcp_established_options(struct sock *sk, struct sk_buff *skb,
745 struct tcp_out_options *opts,
746 struct tcp_md5sig_key **md5)
748 struct tcp_skb_cb *tcb = skb ? TCP_SKB_CB(skb) : NULL;
749 struct tcp_sock *tp = tcp_sk(sk);
750 unsigned int size = 0;
751 unsigned int eff_sacks;
753 #ifdef CONFIG_TCP_MD5SIG
754 *md5 = tp->af_specific->md5_lookup(sk, sk);
755 if (unlikely(*md5)) {
756 opts->options |= OPTION_MD5;
757 size += TCPOLEN_MD5SIG_ALIGNED;
763 if (likely(tp->rx_opt.tstamp_ok)) {
764 opts->options |= OPTION_TS;
765 opts->tsval = tcb ? tcb->when : 0;
766 opts->tsecr = tp->rx_opt.ts_recent;
767 size += TCPOLEN_TSTAMP_ALIGNED;
770 eff_sacks = tp->rx_opt.num_sacks + tp->rx_opt.dsack;
771 if (unlikely(eff_sacks)) {
772 const unsigned int remaining = MAX_TCP_OPTION_SPACE - size;
773 opts->num_sack_blocks =
774 min_t(unsigned int, eff_sacks,
775 (remaining - TCPOLEN_SACK_BASE_ALIGNED) /
776 TCPOLEN_SACK_PERBLOCK);
777 size += TCPOLEN_SACK_BASE_ALIGNED +
778 opts->num_sack_blocks * TCPOLEN_SACK_PERBLOCK;
784 /* This routine actually transmits TCP packets queued in by
785 * tcp_do_sendmsg(). This is used by both the initial
786 * transmission and possible later retransmissions.
787 * All SKB's seen here are completely headerless. It is our
788 * job to build the TCP header, and pass the packet down to
789 * IP so it can do the same plus pass the packet off to the
792 * We are working here with either a clone of the original
793 * SKB, or a fresh unique copy made by the retransmit engine.
795 static int tcp_transmit_skb(struct sock *sk, struct sk_buff *skb, int clone_it,
798 const struct inet_connection_sock *icsk = inet_csk(sk);
799 struct inet_sock *inet;
801 struct tcp_skb_cb *tcb;
802 struct tcp_out_options opts;
803 unsigned int tcp_options_size, tcp_header_size;
804 struct tcp_md5sig_key *md5;
808 BUG_ON(!skb || !tcp_skb_pcount(skb));
810 /* If congestion control is doing timestamping, we must
811 * take such a timestamp before we potentially clone/copy.
813 if (icsk->icsk_ca_ops->flags & TCP_CONG_RTT_STAMP)
814 __net_timestamp(skb);
816 if (likely(clone_it)) {
817 if (unlikely(skb_cloned(skb)))
818 skb = pskb_copy(skb, gfp_mask);
820 skb = skb_clone(skb, gfp_mask);
827 tcb = TCP_SKB_CB(skb);
828 memset(&opts, 0, sizeof(opts));
830 if (unlikely(tcb->tcp_flags & TCPHDR_SYN))
831 tcp_options_size = tcp_syn_options(sk, skb, &opts, &md5);
833 tcp_options_size = tcp_established_options(sk, skb, &opts,
835 tcp_header_size = tcp_options_size + sizeof(struct tcphdr);
837 if (tcp_packets_in_flight(tp) == 0) {
838 tcp_ca_event(sk, CA_EVENT_TX_START);
843 skb_push(skb, tcp_header_size);
844 skb_reset_transport_header(skb);
845 skb_set_owner_w(skb, sk);
847 /* Build TCP header and checksum it. */
849 th->source = inet->inet_sport;
850 th->dest = inet->inet_dport;
851 th->seq = htonl(tcb->seq);
852 th->ack_seq = htonl(tp->rcv_nxt);
853 *(((__be16 *)th) + 6) = htons(((tcp_header_size >> 2) << 12) |
856 if (unlikely(tcb->tcp_flags & TCPHDR_SYN)) {
857 /* RFC1323: The window in SYN & SYN/ACK segments
860 th->window = htons(min(tp->rcv_wnd, 65535U));
862 th->window = htons(tcp_select_window(sk));
867 /* The urg_mode check is necessary during a below snd_una win probe */
868 if (unlikely(tcp_urg_mode(tp) && before(tcb->seq, tp->snd_up))) {
869 if (before(tp->snd_up, tcb->seq + 0x10000)) {
870 th->urg_ptr = htons(tp->snd_up - tcb->seq);
872 } else if (after(tcb->seq + 0xFFFF, tp->snd_nxt)) {
873 th->urg_ptr = htons(0xFFFF);
878 tcp_options_write((__be32 *)(th + 1), tp, &opts);
879 if (likely((tcb->tcp_flags & TCPHDR_SYN) == 0))
880 TCP_ECN_send(sk, skb, tcp_header_size);
882 #ifdef CONFIG_TCP_MD5SIG
883 /* Calculate the MD5 hash, as we have all we need now */
885 sk_nocaps_add(sk, NETIF_F_GSO_MASK);
886 tp->af_specific->calc_md5_hash(opts.hash_location,
891 icsk->icsk_af_ops->send_check(sk, skb);
893 if (likely(tcb->tcp_flags & TCPHDR_ACK))
894 tcp_event_ack_sent(sk, tcp_skb_pcount(skb));
896 if (skb->len != tcp_header_size)
897 tcp_event_data_sent(tp, sk);
899 if (after(tcb->end_seq, tp->snd_nxt) || tcb->seq == tcb->end_seq)
900 TCP_ADD_STATS(sock_net(sk), TCP_MIB_OUTSEGS,
901 tcp_skb_pcount(skb));
903 err = icsk->icsk_af_ops->queue_xmit(skb, &inet->cork.fl);
904 if (likely(err <= 0))
907 tcp_enter_cwr(sk, 1);
909 return net_xmit_eval(err);
912 /* This routine just queues the buffer for sending.
914 * NOTE: probe0 timer is not checked, do not forget tcp_push_pending_frames,
915 * otherwise socket can stall.
917 static void tcp_queue_skb(struct sock *sk, struct sk_buff *skb)
919 struct tcp_sock *tp = tcp_sk(sk);
921 /* Advance write_seq and place onto the write_queue. */
922 tp->write_seq = TCP_SKB_CB(skb)->end_seq;
923 skb_header_release(skb);
924 tcp_add_write_queue_tail(sk, skb);
925 sk->sk_wmem_queued += skb->truesize;
926 sk_mem_charge(sk, skb->truesize);
929 /* Initialize TSO segments for a packet. */
930 static void tcp_set_skb_tso_segs(const struct sock *sk, struct sk_buff *skb,
931 unsigned int mss_now)
933 if (skb->len <= mss_now || !sk_can_gso(sk) ||
934 skb->ip_summed == CHECKSUM_NONE) {
935 /* Avoid the costly divide in the normal
938 skb_shinfo(skb)->gso_segs = 1;
939 skb_shinfo(skb)->gso_size = 0;
940 skb_shinfo(skb)->gso_type = 0;
942 skb_shinfo(skb)->gso_segs = DIV_ROUND_UP(skb->len, mss_now);
943 skb_shinfo(skb)->gso_size = mss_now;
944 skb_shinfo(skb)->gso_type = sk->sk_gso_type;
948 /* When a modification to fackets out becomes necessary, we need to check
949 * skb is counted to fackets_out or not.
951 static void tcp_adjust_fackets_out(struct sock *sk, const struct sk_buff *skb,
954 struct tcp_sock *tp = tcp_sk(sk);
956 if (!tp->sacked_out || tcp_is_reno(tp))
959 if (after(tcp_highest_sack_seq(tp), TCP_SKB_CB(skb)->seq))
960 tp->fackets_out -= decr;
963 /* Pcount in the middle of the write queue got changed, we need to do various
964 * tweaks to fix counters
966 static void tcp_adjust_pcount(struct sock *sk, const struct sk_buff *skb, int decr)
968 struct tcp_sock *tp = tcp_sk(sk);
970 tp->packets_out -= decr;
972 if (TCP_SKB_CB(skb)->sacked & TCPCB_SACKED_ACKED)
973 tp->sacked_out -= decr;
974 if (TCP_SKB_CB(skb)->sacked & TCPCB_SACKED_RETRANS)
975 tp->retrans_out -= decr;
976 if (TCP_SKB_CB(skb)->sacked & TCPCB_LOST)
977 tp->lost_out -= decr;
979 /* Reno case is special. Sigh... */
980 if (tcp_is_reno(tp) && decr > 0)
981 tp->sacked_out -= min_t(u32, tp->sacked_out, decr);
983 tcp_adjust_fackets_out(sk, skb, decr);
985 if (tp->lost_skb_hint &&
986 before(TCP_SKB_CB(skb)->seq, TCP_SKB_CB(tp->lost_skb_hint)->seq) &&
987 (tcp_is_fack(tp) || (TCP_SKB_CB(skb)->sacked & TCPCB_SACKED_ACKED)))
988 tp->lost_cnt_hint -= decr;
990 tcp_verify_left_out(tp);
993 /* Function to create two new TCP segments. Shrinks the given segment
994 * to the specified size and appends a new segment with the rest of the
995 * packet to the list. This won't be called frequently, I hope.
996 * Remember, these are still headerless SKBs at this point.
998 int tcp_fragment(struct sock *sk, struct sk_buff *skb, u32 len,
999 unsigned int mss_now)
1001 struct tcp_sock *tp = tcp_sk(sk);
1002 struct sk_buff *buff;
1003 int nsize, old_factor;
1007 if (WARN_ON(len > skb->len))
1010 nsize = skb_headlen(skb) - len;
1014 if (skb_cloned(skb) &&
1015 skb_is_nonlinear(skb) &&
1016 pskb_expand_head(skb, 0, 0, GFP_ATOMIC))
1019 /* Get a new skb... force flag on. */
1020 buff = sk_stream_alloc_skb(sk, nsize, GFP_ATOMIC);
1022 return -ENOMEM; /* We'll just try again later. */
1024 sk->sk_wmem_queued += buff->truesize;
1025 sk_mem_charge(sk, buff->truesize);
1026 nlen = skb->len - len - nsize;
1027 buff->truesize += nlen;
1028 skb->truesize -= nlen;
1030 /* Correct the sequence numbers. */
1031 TCP_SKB_CB(buff)->seq = TCP_SKB_CB(skb)->seq + len;
1032 TCP_SKB_CB(buff)->end_seq = TCP_SKB_CB(skb)->end_seq;
1033 TCP_SKB_CB(skb)->end_seq = TCP_SKB_CB(buff)->seq;
1035 /* PSH and FIN should only be set in the second packet. */
1036 flags = TCP_SKB_CB(skb)->tcp_flags;
1037 TCP_SKB_CB(skb)->tcp_flags = flags & ~(TCPHDR_FIN | TCPHDR_PSH);
1038 TCP_SKB_CB(buff)->tcp_flags = flags;
1039 TCP_SKB_CB(buff)->sacked = TCP_SKB_CB(skb)->sacked;
1041 if (!skb_shinfo(skb)->nr_frags && skb->ip_summed != CHECKSUM_PARTIAL) {
1042 /* Copy and checksum data tail into the new buffer. */
1043 buff->csum = csum_partial_copy_nocheck(skb->data + len,
1044 skb_put(buff, nsize),
1049 skb->csum = csum_block_sub(skb->csum, buff->csum, len);
1051 skb->ip_summed = CHECKSUM_PARTIAL;
1052 skb_split(skb, buff, len);
1055 buff->ip_summed = skb->ip_summed;
1057 /* Looks stupid, but our code really uses when of
1058 * skbs, which it never sent before. --ANK
1060 TCP_SKB_CB(buff)->when = TCP_SKB_CB(skb)->when;
1061 buff->tstamp = skb->tstamp;
1063 old_factor = tcp_skb_pcount(skb);
1065 /* Fix up tso_factor for both original and new SKB. */
1066 tcp_set_skb_tso_segs(sk, skb, mss_now);
1067 tcp_set_skb_tso_segs(sk, buff, mss_now);
1069 /* If this packet has been sent out already, we must
1070 * adjust the various packet counters.
1072 if (!before(tp->snd_nxt, TCP_SKB_CB(buff)->end_seq)) {
1073 int diff = old_factor - tcp_skb_pcount(skb) -
1074 tcp_skb_pcount(buff);
1077 tcp_adjust_pcount(sk, skb, diff);
1080 /* Link BUFF into the send queue. */
1081 skb_header_release(buff);
1082 tcp_insert_write_queue_after(skb, buff, sk);
1087 /* This is similar to __pskb_pull_head() (it will go to core/skbuff.c
1088 * eventually). The difference is that pulled data not copied, but
1089 * immediately discarded.
1091 static void __pskb_trim_head(struct sk_buff *skb, int len)
1095 eat = min_t(int, len, skb_headlen(skb));
1097 __skb_pull(skb, eat);
1098 skb->avail_size -= eat;
1105 for (i = 0; i < skb_shinfo(skb)->nr_frags; i++) {
1106 int size = skb_frag_size(&skb_shinfo(skb)->frags[i]);
1109 skb_frag_unref(skb, i);
1112 skb_shinfo(skb)->frags[k] = skb_shinfo(skb)->frags[i];
1114 skb_shinfo(skb)->frags[k].page_offset += eat;
1115 skb_frag_size_sub(&skb_shinfo(skb)->frags[k], eat);
1121 skb_shinfo(skb)->nr_frags = k;
1123 skb_reset_tail_pointer(skb);
1124 skb->data_len -= len;
1125 skb->len = skb->data_len;
1128 /* Remove acked data from a packet in the transmit queue. */
1129 int tcp_trim_head(struct sock *sk, struct sk_buff *skb, u32 len)
1131 if (skb_cloned(skb) && pskb_expand_head(skb, 0, 0, GFP_ATOMIC))
1134 __pskb_trim_head(skb, len);
1136 TCP_SKB_CB(skb)->seq += len;
1137 skb->ip_summed = CHECKSUM_PARTIAL;
1139 skb->truesize -= len;
1140 sk->sk_wmem_queued -= len;
1141 sk_mem_uncharge(sk, len);
1142 sock_set_flag(sk, SOCK_QUEUE_SHRUNK);
1144 /* Any change of skb->len requires recalculation of tso factor. */
1145 if (tcp_skb_pcount(skb) > 1)
1146 tcp_set_skb_tso_segs(sk, skb, tcp_skb_mss(skb));
1151 /* Calculate MSS. Not accounting for SACKs here. */
1152 int tcp_mtu_to_mss(struct sock *sk, int pmtu)
1154 const struct tcp_sock *tp = tcp_sk(sk);
1155 const struct inet_connection_sock *icsk = inet_csk(sk);
1158 /* Calculate base mss without TCP options:
1159 It is MMS_S - sizeof(tcphdr) of rfc1122
1161 mss_now = pmtu - icsk->icsk_af_ops->net_header_len - sizeof(struct tcphdr);
1163 /* IPv6 adds a frag_hdr in case RTAX_FEATURE_ALLFRAG is set */
1164 if (icsk->icsk_af_ops->net_frag_header_len) {
1165 const struct dst_entry *dst = __sk_dst_get(sk);
1167 if (dst && dst_allfrag(dst))
1168 mss_now -= icsk->icsk_af_ops->net_frag_header_len;
1171 /* Clamp it (mss_clamp does not include tcp options) */
1172 if (mss_now > tp->rx_opt.mss_clamp)
1173 mss_now = tp->rx_opt.mss_clamp;
1175 /* Now subtract optional transport overhead */
1176 mss_now -= icsk->icsk_ext_hdr_len;
1178 /* Then reserve room for full set of TCP options and 8 bytes of data */
1182 /* Now subtract TCP options size, not including SACKs */
1183 mss_now -= tp->tcp_header_len - sizeof(struct tcphdr);
1188 /* Inverse of above */
1189 int tcp_mss_to_mtu(struct sock *sk, int mss)
1191 const struct tcp_sock *tp = tcp_sk(sk);
1192 const struct inet_connection_sock *icsk = inet_csk(sk);
1196 tp->tcp_header_len +
1197 icsk->icsk_ext_hdr_len +
1198 icsk->icsk_af_ops->net_header_len;
1200 /* IPv6 adds a frag_hdr in case RTAX_FEATURE_ALLFRAG is set */
1201 if (icsk->icsk_af_ops->net_frag_header_len) {
1202 const struct dst_entry *dst = __sk_dst_get(sk);
1204 if (dst && dst_allfrag(dst))
1205 mtu += icsk->icsk_af_ops->net_frag_header_len;
1210 /* MTU probing init per socket */
1211 void tcp_mtup_init(struct sock *sk)
1213 struct tcp_sock *tp = tcp_sk(sk);
1214 struct inet_connection_sock *icsk = inet_csk(sk);
1216 icsk->icsk_mtup.enabled = sysctl_tcp_mtu_probing > 1;
1217 icsk->icsk_mtup.search_high = tp->rx_opt.mss_clamp + sizeof(struct tcphdr) +
1218 icsk->icsk_af_ops->net_header_len;
1219 icsk->icsk_mtup.search_low = tcp_mss_to_mtu(sk, sysctl_tcp_base_mss);
1220 icsk->icsk_mtup.probe_size = 0;
1222 EXPORT_SYMBOL(tcp_mtup_init);
1224 /* This function synchronize snd mss to current pmtu/exthdr set.
1226 tp->rx_opt.user_mss is mss set by user by TCP_MAXSEG. It does NOT counts
1227 for TCP options, but includes only bare TCP header.
1229 tp->rx_opt.mss_clamp is mss negotiated at connection setup.
1230 It is minimum of user_mss and mss received with SYN.
1231 It also does not include TCP options.
1233 inet_csk(sk)->icsk_pmtu_cookie is last pmtu, seen by this function.
1235 tp->mss_cache is current effective sending mss, including
1236 all tcp options except for SACKs. It is evaluated,
1237 taking into account current pmtu, but never exceeds
1238 tp->rx_opt.mss_clamp.
1240 NOTE1. rfc1122 clearly states that advertised MSS
1241 DOES NOT include either tcp or ip options.
1243 NOTE2. inet_csk(sk)->icsk_pmtu_cookie and tp->mss_cache
1244 are READ ONLY outside this function. --ANK (980731)
1246 unsigned int tcp_sync_mss(struct sock *sk, u32 pmtu)
1248 struct tcp_sock *tp = tcp_sk(sk);
1249 struct inet_connection_sock *icsk = inet_csk(sk);
1252 if (icsk->icsk_mtup.search_high > pmtu)
1253 icsk->icsk_mtup.search_high = pmtu;
1255 mss_now = tcp_mtu_to_mss(sk, pmtu);
1256 mss_now = tcp_bound_to_half_wnd(tp, mss_now);
1258 /* And store cached results */
1259 icsk->icsk_pmtu_cookie = pmtu;
1260 if (icsk->icsk_mtup.enabled)
1261 mss_now = min(mss_now, tcp_mtu_to_mss(sk, icsk->icsk_mtup.search_low));
1262 tp->mss_cache = mss_now;
1266 EXPORT_SYMBOL(tcp_sync_mss);
1268 /* Compute the current effective MSS, taking SACKs and IP options,
1269 * and even PMTU discovery events into account.
1271 unsigned int tcp_current_mss(struct sock *sk)
1273 const struct tcp_sock *tp = tcp_sk(sk);
1274 const struct dst_entry *dst = __sk_dst_get(sk);
1276 unsigned int header_len;
1277 struct tcp_out_options opts;
1278 struct tcp_md5sig_key *md5;
1280 mss_now = tp->mss_cache;
1283 u32 mtu = dst_mtu(dst);
1284 if (mtu != inet_csk(sk)->icsk_pmtu_cookie)
1285 mss_now = tcp_sync_mss(sk, mtu);
1288 header_len = tcp_established_options(sk, NULL, &opts, &md5) +
1289 sizeof(struct tcphdr);
1290 /* The mss_cache is sized based on tp->tcp_header_len, which assumes
1291 * some common options. If this is an odd packet (because we have SACK
1292 * blocks etc) then our calculated header_len will be different, and
1293 * we have to adjust mss_now correspondingly */
1294 if (header_len != tp->tcp_header_len) {
1295 int delta = (int) header_len - tp->tcp_header_len;
1302 /* Congestion window validation. (RFC2861) */
1303 static void tcp_cwnd_validate(struct sock *sk)
1305 struct tcp_sock *tp = tcp_sk(sk);
1307 if (tp->packets_out >= tp->snd_cwnd) {
1308 /* Network is feed fully. */
1309 tp->snd_cwnd_used = 0;
1310 tp->snd_cwnd_stamp = tcp_time_stamp;
1312 /* Network starves. */
1313 if (tp->packets_out > tp->snd_cwnd_used)
1314 tp->snd_cwnd_used = tp->packets_out;
1316 if (sysctl_tcp_slow_start_after_idle &&
1317 (s32)(tcp_time_stamp - tp->snd_cwnd_stamp) >= inet_csk(sk)->icsk_rto)
1318 tcp_cwnd_application_limited(sk);
1322 /* Returns the portion of skb which can be sent right away without
1323 * introducing MSS oddities to segment boundaries. In rare cases where
1324 * mss_now != mss_cache, we will request caller to create a small skb
1325 * per input skb which could be mostly avoided here (if desired).
1327 * We explicitly want to create a request for splitting write queue tail
1328 * to a small skb for Nagle purposes while avoiding unnecessary modulos,
1329 * thus all the complexity (cwnd_len is always MSS multiple which we
1330 * return whenever allowed by the other factors). Basically we need the
1331 * modulo only when the receiver window alone is the limiting factor or
1332 * when we would be allowed to send the split-due-to-Nagle skb fully.
1334 static unsigned int tcp_mss_split_point(const struct sock *sk, const struct sk_buff *skb,
1335 unsigned int mss_now, unsigned int cwnd)
1337 const struct tcp_sock *tp = tcp_sk(sk);
1338 u32 needed, window, cwnd_len;
1340 window = tcp_wnd_end(tp) - TCP_SKB_CB(skb)->seq;
1341 cwnd_len = mss_now * cwnd;
1343 if (likely(cwnd_len <= window && skb != tcp_write_queue_tail(sk)))
1346 needed = min(skb->len, window);
1348 if (cwnd_len <= needed)
1351 return needed - needed % mss_now;
1354 /* Can at least one segment of SKB be sent right now, according to the
1355 * congestion window rules? If so, return how many segments are allowed.
1357 static inline unsigned int tcp_cwnd_test(const struct tcp_sock *tp,
1358 const struct sk_buff *skb)
1360 u32 in_flight, cwnd;
1362 /* Don't be strict about the congestion window for the final FIN. */
1363 if ((TCP_SKB_CB(skb)->tcp_flags & TCPHDR_FIN) &&
1364 tcp_skb_pcount(skb) == 1)
1367 in_flight = tcp_packets_in_flight(tp);
1368 cwnd = tp->snd_cwnd;
1369 if (in_flight < cwnd)
1370 return (cwnd - in_flight);
1375 /* Initialize TSO state of a skb.
1376 * This must be invoked the first time we consider transmitting
1377 * SKB onto the wire.
1379 static int tcp_init_tso_segs(const struct sock *sk, struct sk_buff *skb,
1380 unsigned int mss_now)
1382 int tso_segs = tcp_skb_pcount(skb);
1384 if (!tso_segs || (tso_segs > 1 && tcp_skb_mss(skb) != mss_now)) {
1385 tcp_set_skb_tso_segs(sk, skb, mss_now);
1386 tso_segs = tcp_skb_pcount(skb);
1391 /* Minshall's variant of the Nagle send check. */
1392 static inline int tcp_minshall_check(const struct tcp_sock *tp)
1394 return after(tp->snd_sml, tp->snd_una) &&
1395 !after(tp->snd_sml, tp->snd_nxt);
1398 /* Return 0, if packet can be sent now without violation Nagle's rules:
1399 * 1. It is full sized.
1400 * 2. Or it contains FIN. (already checked by caller)
1401 * 3. Or TCP_CORK is not set, and TCP_NODELAY is set.
1402 * 4. Or TCP_CORK is not set, and all sent packets are ACKed.
1403 * With Minshall's modification: all sent small packets are ACKed.
1405 static inline int tcp_nagle_check(const struct tcp_sock *tp,
1406 const struct sk_buff *skb,
1407 unsigned int mss_now, int nonagle)
1409 return skb->len < mss_now &&
1410 ((nonagle & TCP_NAGLE_CORK) ||
1411 (!nonagle && tp->packets_out && tcp_minshall_check(tp)));
1414 /* Return non-zero if the Nagle test allows this packet to be
1417 static inline int tcp_nagle_test(const struct tcp_sock *tp, const struct sk_buff *skb,
1418 unsigned int cur_mss, int nonagle)
1420 /* Nagle rule does not apply to frames, which sit in the middle of the
1421 * write_queue (they have no chances to get new data).
1423 * This is implemented in the callers, where they modify the 'nonagle'
1424 * argument based upon the location of SKB in the send queue.
1426 if (nonagle & TCP_NAGLE_PUSH)
1429 /* Don't use the nagle rule for urgent data (or for the final FIN).
1430 * Nagle can be ignored during F-RTO too (see RFC4138).
1432 if (tcp_urg_mode(tp) || (tp->frto_counter == 2) ||
1433 (TCP_SKB_CB(skb)->tcp_flags & TCPHDR_FIN))
1436 if (!tcp_nagle_check(tp, skb, cur_mss, nonagle))
1442 /* Does at least the first segment of SKB fit into the send window? */
1443 static inline int tcp_snd_wnd_test(const struct tcp_sock *tp, const struct sk_buff *skb,
1444 unsigned int cur_mss)
1446 u32 end_seq = TCP_SKB_CB(skb)->end_seq;
1448 if (skb->len > cur_mss)
1449 end_seq = TCP_SKB_CB(skb)->seq + cur_mss;
1451 return !after(end_seq, tcp_wnd_end(tp));
1454 /* This checks if the data bearing packet SKB (usually tcp_send_head(sk))
1455 * should be put on the wire right now. If so, it returns the number of
1456 * packets allowed by the congestion window.
1458 static unsigned int tcp_snd_test(const struct sock *sk, struct sk_buff *skb,
1459 unsigned int cur_mss, int nonagle)
1461 const struct tcp_sock *tp = tcp_sk(sk);
1462 unsigned int cwnd_quota;
1464 tcp_init_tso_segs(sk, skb, cur_mss);
1466 if (!tcp_nagle_test(tp, skb, cur_mss, nonagle))
1469 cwnd_quota = tcp_cwnd_test(tp, skb);
1470 if (cwnd_quota && !tcp_snd_wnd_test(tp, skb, cur_mss))
1476 /* Test if sending is allowed right now. */
1477 int tcp_may_send_now(struct sock *sk)
1479 const struct tcp_sock *tp = tcp_sk(sk);
1480 struct sk_buff *skb = tcp_send_head(sk);
1483 tcp_snd_test(sk, skb, tcp_current_mss(sk),
1484 (tcp_skb_is_last(sk, skb) ?
1485 tp->nonagle : TCP_NAGLE_PUSH));
1488 /* Trim TSO SKB to LEN bytes, put the remaining data into a new packet
1489 * which is put after SKB on the list. It is very much like
1490 * tcp_fragment() except that it may make several kinds of assumptions
1491 * in order to speed up the splitting operation. In particular, we
1492 * know that all the data is in scatter-gather pages, and that the
1493 * packet has never been sent out before (and thus is not cloned).
1495 static int tso_fragment(struct sock *sk, struct sk_buff *skb, unsigned int len,
1496 unsigned int mss_now, gfp_t gfp)
1498 struct sk_buff *buff;
1499 int nlen = skb->len - len;
1502 /* All of a TSO frame must be composed of paged data. */
1503 if (skb->len != skb->data_len)
1504 return tcp_fragment(sk, skb, len, mss_now);
1506 buff = sk_stream_alloc_skb(sk, 0, gfp);
1507 if (unlikely(buff == NULL))
1510 sk->sk_wmem_queued += buff->truesize;
1511 sk_mem_charge(sk, buff->truesize);
1512 buff->truesize += nlen;
1513 skb->truesize -= nlen;
1515 /* Correct the sequence numbers. */
1516 TCP_SKB_CB(buff)->seq = TCP_SKB_CB(skb)->seq + len;
1517 TCP_SKB_CB(buff)->end_seq = TCP_SKB_CB(skb)->end_seq;
1518 TCP_SKB_CB(skb)->end_seq = TCP_SKB_CB(buff)->seq;
1520 /* PSH and FIN should only be set in the second packet. */
1521 flags = TCP_SKB_CB(skb)->tcp_flags;
1522 TCP_SKB_CB(skb)->tcp_flags = flags & ~(TCPHDR_FIN | TCPHDR_PSH);
1523 TCP_SKB_CB(buff)->tcp_flags = flags;
1525 /* This packet was never sent out yet, so no SACK bits. */
1526 TCP_SKB_CB(buff)->sacked = 0;
1528 buff->ip_summed = skb->ip_summed = CHECKSUM_PARTIAL;
1529 skb_split(skb, buff, len);
1531 /* Fix up tso_factor for both original and new SKB. */
1532 tcp_set_skb_tso_segs(sk, skb, mss_now);
1533 tcp_set_skb_tso_segs(sk, buff, mss_now);
1535 /* Link BUFF into the send queue. */
1536 skb_header_release(buff);
1537 tcp_insert_write_queue_after(skb, buff, sk);
1542 /* Try to defer sending, if possible, in order to minimize the amount
1543 * of TSO splitting we do. View it as a kind of TSO Nagle test.
1545 * This algorithm is from John Heffner.
1547 static int tcp_tso_should_defer(struct sock *sk, struct sk_buff *skb)
1549 struct tcp_sock *tp = tcp_sk(sk);
1550 const struct inet_connection_sock *icsk = inet_csk(sk);
1551 u32 send_win, cong_win, limit, in_flight;
1554 if (TCP_SKB_CB(skb)->tcp_flags & TCPHDR_FIN)
1557 if (icsk->icsk_ca_state != TCP_CA_Open)
1560 /* Defer for less than two clock ticks. */
1561 if (tp->tso_deferred &&
1562 (((u32)jiffies << 1) >> 1) - (tp->tso_deferred >> 1) > 1)
1565 in_flight = tcp_packets_in_flight(tp);
1567 BUG_ON(tcp_skb_pcount(skb) <= 1 || (tp->snd_cwnd <= in_flight));
1569 send_win = tcp_wnd_end(tp) - TCP_SKB_CB(skb)->seq;
1571 /* From in_flight test above, we know that cwnd > in_flight. */
1572 cong_win = (tp->snd_cwnd - in_flight) * tp->mss_cache;
1574 limit = min(send_win, cong_win);
1576 /* If a full-sized TSO skb can be sent, do it. */
1577 if (limit >= sk->sk_gso_max_size)
1580 /* Middle in queue won't get any more data, full sendable already? */
1581 if ((skb != tcp_write_queue_tail(sk)) && (limit >= skb->len))
1584 win_divisor = ACCESS_ONCE(sysctl_tcp_tso_win_divisor);
1586 u32 chunk = min(tp->snd_wnd, tp->snd_cwnd * tp->mss_cache);
1588 /* If at least some fraction of a window is available,
1591 chunk /= win_divisor;
1595 /* Different approach, try not to defer past a single
1596 * ACK. Receiver should ACK every other full sized
1597 * frame, so if we have space for more than 3 frames
1600 if (limit > tcp_max_tso_deferred_mss(tp) * tp->mss_cache)
1604 /* Ok, it looks like it is advisable to defer. */
1605 tp->tso_deferred = 1 | (jiffies << 1);
1610 tp->tso_deferred = 0;
1614 /* Create a new MTU probe if we are ready.
1615 * MTU probe is regularly attempting to increase the path MTU by
1616 * deliberately sending larger packets. This discovers routing
1617 * changes resulting in larger path MTUs.
1619 * Returns 0 if we should wait to probe (no cwnd available),
1620 * 1 if a probe was sent,
1623 static int tcp_mtu_probe(struct sock *sk)
1625 struct tcp_sock *tp = tcp_sk(sk);
1626 struct inet_connection_sock *icsk = inet_csk(sk);
1627 struct sk_buff *skb, *nskb, *next;
1634 /* Not currently probing/verifying,
1636 * have enough cwnd, and
1637 * not SACKing (the variable headers throw things off) */
1638 if (!icsk->icsk_mtup.enabled ||
1639 icsk->icsk_mtup.probe_size ||
1640 inet_csk(sk)->icsk_ca_state != TCP_CA_Open ||
1641 tp->snd_cwnd < 11 ||
1642 tp->rx_opt.num_sacks || tp->rx_opt.dsack)
1645 /* Very simple search strategy: just double the MSS. */
1646 mss_now = tcp_current_mss(sk);
1647 probe_size = 2 * tp->mss_cache;
1648 size_needed = probe_size + (tp->reordering + 1) * tp->mss_cache;
1649 if (probe_size > tcp_mtu_to_mss(sk, icsk->icsk_mtup.search_high)) {
1650 /* TODO: set timer for probe_converge_event */
1654 /* Have enough data in the send queue to probe? */
1655 if (tp->write_seq - tp->snd_nxt < size_needed)
1658 if (tp->snd_wnd < size_needed)
1660 if (after(tp->snd_nxt + size_needed, tcp_wnd_end(tp)))
1663 /* Do we need to wait to drain cwnd? With none in flight, don't stall */
1664 if (tcp_packets_in_flight(tp) + 2 > tp->snd_cwnd) {
1665 if (!tcp_packets_in_flight(tp))
1671 /* We're allowed to probe. Build it now. */
1672 if ((nskb = sk_stream_alloc_skb(sk, probe_size, GFP_ATOMIC)) == NULL)
1674 sk->sk_wmem_queued += nskb->truesize;
1675 sk_mem_charge(sk, nskb->truesize);
1677 skb = tcp_send_head(sk);
1679 TCP_SKB_CB(nskb)->seq = TCP_SKB_CB(skb)->seq;
1680 TCP_SKB_CB(nskb)->end_seq = TCP_SKB_CB(skb)->seq + probe_size;
1681 TCP_SKB_CB(nskb)->tcp_flags = TCPHDR_ACK;
1682 TCP_SKB_CB(nskb)->sacked = 0;
1684 nskb->ip_summed = skb->ip_summed;
1686 tcp_insert_write_queue_before(nskb, skb, sk);
1689 tcp_for_write_queue_from_safe(skb, next, sk) {
1690 copy = min_t(int, skb->len, probe_size - len);
1691 if (nskb->ip_summed)
1692 skb_copy_bits(skb, 0, skb_put(nskb, copy), copy);
1694 nskb->csum = skb_copy_and_csum_bits(skb, 0,
1695 skb_put(nskb, copy),
1698 if (skb->len <= copy) {
1699 /* We've eaten all the data from this skb.
1701 TCP_SKB_CB(nskb)->tcp_flags |= TCP_SKB_CB(skb)->tcp_flags;
1702 tcp_unlink_write_queue(skb, sk);
1703 sk_wmem_free_skb(sk, skb);
1705 TCP_SKB_CB(nskb)->tcp_flags |= TCP_SKB_CB(skb)->tcp_flags &
1706 ~(TCPHDR_FIN|TCPHDR_PSH);
1707 if (!skb_shinfo(skb)->nr_frags) {
1708 skb_pull(skb, copy);
1709 if (skb->ip_summed != CHECKSUM_PARTIAL)
1710 skb->csum = csum_partial(skb->data,
1713 __pskb_trim_head(skb, copy);
1714 tcp_set_skb_tso_segs(sk, skb, mss_now);
1716 TCP_SKB_CB(skb)->seq += copy;
1721 if (len >= probe_size)
1724 tcp_init_tso_segs(sk, nskb, nskb->len);
1726 /* We're ready to send. If this fails, the probe will
1727 * be resegmented into mss-sized pieces by tcp_write_xmit(). */
1728 TCP_SKB_CB(nskb)->when = tcp_time_stamp;
1729 if (!tcp_transmit_skb(sk, nskb, 1, GFP_ATOMIC)) {
1730 /* Decrement cwnd here because we are sending
1731 * effectively two packets. */
1733 tcp_event_new_data_sent(sk, nskb);
1735 icsk->icsk_mtup.probe_size = tcp_mss_to_mtu(sk, nskb->len);
1736 tp->mtu_probe.probe_seq_start = TCP_SKB_CB(nskb)->seq;
1737 tp->mtu_probe.probe_seq_end = TCP_SKB_CB(nskb)->end_seq;
1745 /* This routine writes packets to the network. It advances the
1746 * send_head. This happens as incoming acks open up the remote
1749 * LARGESEND note: !tcp_urg_mode is overkill, only frames between
1750 * snd_up-64k-mss .. snd_up cannot be large. However, taking into
1751 * account rare use of URG, this is not a big flaw.
1753 * Returns 1, if no segments are in flight and we have queued segments, but
1754 * cannot send anything now because of SWS or another problem.
1756 static int tcp_write_xmit(struct sock *sk, unsigned int mss_now, int nonagle,
1757 int push_one, gfp_t gfp)
1759 struct tcp_sock *tp = tcp_sk(sk);
1760 struct sk_buff *skb;
1761 unsigned int tso_segs, sent_pkts;
1768 /* Do MTU probing. */
1769 result = tcp_mtu_probe(sk);
1772 } else if (result > 0) {
1777 while ((skb = tcp_send_head(sk))) {
1780 tso_segs = tcp_init_tso_segs(sk, skb, mss_now);
1783 cwnd_quota = tcp_cwnd_test(tp, skb);
1787 if (unlikely(!tcp_snd_wnd_test(tp, skb, mss_now)))
1790 if (tso_segs == 1) {
1791 if (unlikely(!tcp_nagle_test(tp, skb, mss_now,
1792 (tcp_skb_is_last(sk, skb) ?
1793 nonagle : TCP_NAGLE_PUSH))))
1796 if (!push_one && tcp_tso_should_defer(sk, skb))
1801 if (tso_segs > 1 && !tcp_urg_mode(tp))
1802 limit = tcp_mss_split_point(sk, skb, mss_now,
1805 if (skb->len > limit &&
1806 unlikely(tso_fragment(sk, skb, limit, mss_now, gfp)))
1809 TCP_SKB_CB(skb)->when = tcp_time_stamp;
1811 if (unlikely(tcp_transmit_skb(sk, skb, 1, gfp)))
1814 /* Advance the send_head. This one is sent out.
1815 * This call will increment packets_out.
1817 tcp_event_new_data_sent(sk, skb);
1819 tcp_minshall_update(tp, mss_now, skb);
1820 sent_pkts += tcp_skb_pcount(skb);
1825 if (inet_csk(sk)->icsk_ca_state == TCP_CA_Recovery)
1826 tp->prr_out += sent_pkts;
1828 if (likely(sent_pkts)) {
1829 tcp_cwnd_validate(sk);
1832 return !tp->packets_out && tcp_send_head(sk);
1835 /* Push out any pending frames which were held back due to
1836 * TCP_CORK or attempt at coalescing tiny packets.
1837 * The socket must be locked by the caller.
1839 void __tcp_push_pending_frames(struct sock *sk, unsigned int cur_mss,
1842 /* If we are closed, the bytes will have to remain here.
1843 * In time closedown will finish, we empty the write queue and
1844 * all will be happy.
1846 if (unlikely(sk->sk_state == TCP_CLOSE))
1849 if (tcp_write_xmit(sk, cur_mss, nonagle, 0, GFP_ATOMIC))
1850 tcp_check_probe_timer(sk);
1853 /* Send _single_ skb sitting at the send head. This function requires
1854 * true push pending frames to setup probe timer etc.
1856 void tcp_push_one(struct sock *sk, unsigned int mss_now)
1858 struct sk_buff *skb = tcp_send_head(sk);
1860 BUG_ON(!skb || skb->len < mss_now);
1862 tcp_write_xmit(sk, mss_now, TCP_NAGLE_PUSH, 1, sk->sk_allocation);
1865 /* This function returns the amount that we can raise the
1866 * usable window based on the following constraints
1868 * 1. The window can never be shrunk once it is offered (RFC 793)
1869 * 2. We limit memory per socket
1872 * "the suggested [SWS] avoidance algorithm for the receiver is to keep
1873 * RECV.NEXT + RCV.WIN fixed until:
1874 * RCV.BUFF - RCV.USER - RCV.WINDOW >= min(1/2 RCV.BUFF, MSS)"
1876 * i.e. don't raise the right edge of the window until you can raise
1877 * it at least MSS bytes.
1879 * Unfortunately, the recommended algorithm breaks header prediction,
1880 * since header prediction assumes th->window stays fixed.
1882 * Strictly speaking, keeping th->window fixed violates the receiver
1883 * side SWS prevention criteria. The problem is that under this rule
1884 * a stream of single byte packets will cause the right side of the
1885 * window to always advance by a single byte.
1887 * Of course, if the sender implements sender side SWS prevention
1888 * then this will not be a problem.
1890 * BSD seems to make the following compromise:
1892 * If the free space is less than the 1/4 of the maximum
1893 * space available and the free space is less than 1/2 mss,
1894 * then set the window to 0.
1895 * [ Actually, bsd uses MSS and 1/4 of maximal _window_ ]
1896 * Otherwise, just prevent the window from shrinking
1897 * and from being larger than the largest representable value.
1899 * This prevents incremental opening of the window in the regime
1900 * where TCP is limited by the speed of the reader side taking
1901 * data out of the TCP receive queue. It does nothing about
1902 * those cases where the window is constrained on the sender side
1903 * because the pipeline is full.
1905 * BSD also seems to "accidentally" limit itself to windows that are a
1906 * multiple of MSS, at least until the free space gets quite small.
1907 * This would appear to be a side effect of the mbuf implementation.
1908 * Combining these two algorithms results in the observed behavior
1909 * of having a fixed window size at almost all times.
1911 * Below we obtain similar behavior by forcing the offered window to
1912 * a multiple of the mss when it is feasible to do so.
1914 * Note, we don't "adjust" for TIMESTAMP or SACK option bytes.
1915 * Regular options like TIMESTAMP are taken into account.
1917 u32 __tcp_select_window(struct sock *sk)
1919 struct inet_connection_sock *icsk = inet_csk(sk);
1920 struct tcp_sock *tp = tcp_sk(sk);
1921 /* MSS for the peer's data. Previous versions used mss_clamp
1922 * here. I don't know if the value based on our guesses
1923 * of peer's MSS is better for the performance. It's more correct
1924 * but may be worse for the performance because of rcv_mss
1925 * fluctuations. --SAW 1998/11/1
1927 int mss = icsk->icsk_ack.rcv_mss;
1928 int free_space = tcp_space(sk);
1929 int full_space = min_t(int, tp->window_clamp, tcp_full_space(sk));
1932 if (mss > full_space)
1935 if (free_space < (full_space >> 1)) {
1936 icsk->icsk_ack.quick = 0;
1938 if (sk_under_memory_pressure(sk))
1939 tp->rcv_ssthresh = min(tp->rcv_ssthresh,
1942 if (free_space < mss)
1946 if (free_space > tp->rcv_ssthresh)
1947 free_space = tp->rcv_ssthresh;
1949 /* Don't do rounding if we are using window scaling, since the
1950 * scaled window will not line up with the MSS boundary anyway.
1952 window = tp->rcv_wnd;
1953 if (tp->rx_opt.rcv_wscale) {
1954 window = free_space;
1956 /* Advertise enough space so that it won't get scaled away.
1957 * Import case: prevent zero window announcement if
1958 * 1<<rcv_wscale > mss.
1960 if (((window >> tp->rx_opt.rcv_wscale) << tp->rx_opt.rcv_wscale) != window)
1961 window = (((window >> tp->rx_opt.rcv_wscale) + 1)
1962 << tp->rx_opt.rcv_wscale);
1964 /* Get the largest window that is a nice multiple of mss.
1965 * Window clamp already applied above.
1966 * If our current window offering is within 1 mss of the
1967 * free space we just keep it. This prevents the divide
1968 * and multiply from happening most of the time.
1969 * We also don't do any window rounding when the free space
1972 if (window <= free_space - mss || window > free_space)
1973 window = (free_space / mss) * mss;
1974 else if (mss == full_space &&
1975 free_space > window + (full_space >> 1))
1976 window = free_space;
1982 /* Collapses two adjacent SKB's during retransmission. */
1983 static void tcp_collapse_retrans(struct sock *sk, struct sk_buff *skb)
1985 struct tcp_sock *tp = tcp_sk(sk);
1986 struct sk_buff *next_skb = tcp_write_queue_next(sk, skb);
1987 int skb_size, next_skb_size;
1989 skb_size = skb->len;
1990 next_skb_size = next_skb->len;
1992 BUG_ON(tcp_skb_pcount(skb) != 1 || tcp_skb_pcount(next_skb) != 1);
1994 tcp_highest_sack_combine(sk, next_skb, skb);
1996 tcp_unlink_write_queue(next_skb, sk);
1998 skb_copy_from_linear_data(next_skb, skb_put(skb, next_skb_size),
2001 if (next_skb->ip_summed == CHECKSUM_PARTIAL)
2002 skb->ip_summed = CHECKSUM_PARTIAL;
2004 if (skb->ip_summed != CHECKSUM_PARTIAL)
2005 skb->csum = csum_block_add(skb->csum, next_skb->csum, skb_size);
2007 /* Update sequence range on original skb. */
2008 TCP_SKB_CB(skb)->end_seq = TCP_SKB_CB(next_skb)->end_seq;
2010 /* Merge over control information. This moves PSH/FIN etc. over */
2011 TCP_SKB_CB(skb)->tcp_flags |= TCP_SKB_CB(next_skb)->tcp_flags;
2013 /* All done, get rid of second SKB and account for it so
2014 * packet counting does not break.
2016 TCP_SKB_CB(skb)->sacked |= TCP_SKB_CB(next_skb)->sacked & TCPCB_EVER_RETRANS;
2018 /* changed transmit queue under us so clear hints */
2019 tcp_clear_retrans_hints_partial(tp);
2020 if (next_skb == tp->retransmit_skb_hint)
2021 tp->retransmit_skb_hint = skb;
2023 tcp_adjust_pcount(sk, next_skb, tcp_skb_pcount(next_skb));
2025 sk_wmem_free_skb(sk, next_skb);
2028 /* Check if coalescing SKBs is legal. */
2029 static int tcp_can_collapse(const struct sock *sk, const struct sk_buff *skb)
2031 if (tcp_skb_pcount(skb) > 1)
2033 /* TODO: SACK collapsing could be used to remove this condition */
2034 if (skb_shinfo(skb)->nr_frags != 0)
2036 if (skb_cloned(skb))
2038 if (skb == tcp_send_head(sk))
2040 /* Some heurestics for collapsing over SACK'd could be invented */
2041 if (TCP_SKB_CB(skb)->sacked & TCPCB_SACKED_ACKED)
2047 /* Collapse packets in the retransmit queue to make to create
2048 * less packets on the wire. This is only done on retransmission.
2050 static void tcp_retrans_try_collapse(struct sock *sk, struct sk_buff *to,
2053 struct tcp_sock *tp = tcp_sk(sk);
2054 struct sk_buff *skb = to, *tmp;
2057 if (!sysctl_tcp_retrans_collapse)
2059 if (TCP_SKB_CB(skb)->tcp_flags & TCPHDR_SYN)
2062 tcp_for_write_queue_from_safe(skb, tmp, sk) {
2063 if (!tcp_can_collapse(sk, skb))
2075 /* Punt if not enough space exists in the first SKB for
2076 * the data in the second
2078 if (skb->len > skb_availroom(to))
2081 if (after(TCP_SKB_CB(skb)->end_seq, tcp_wnd_end(tp)))
2084 tcp_collapse_retrans(sk, to);
2088 /* This retransmits one SKB. Policy decisions and retransmit queue
2089 * state updates are done by the caller. Returns non-zero if an
2090 * error occurred which prevented the send.
2092 int tcp_retransmit_skb(struct sock *sk, struct sk_buff *skb)
2094 struct tcp_sock *tp = tcp_sk(sk);
2095 struct inet_connection_sock *icsk = inet_csk(sk);
2096 unsigned int cur_mss;
2099 /* Inconslusive MTU probe */
2100 if (icsk->icsk_mtup.probe_size) {
2101 icsk->icsk_mtup.probe_size = 0;
2104 /* Do not sent more than we queued. 1/4 is reserved for possible
2105 * copying overhead: fragmentation, tunneling, mangling etc.
2107 if (atomic_read(&sk->sk_wmem_alloc) >
2108 min(sk->sk_wmem_queued + (sk->sk_wmem_queued >> 2), sk->sk_sndbuf))
2111 if (before(TCP_SKB_CB(skb)->seq, tp->snd_una)) {
2112 if (before(TCP_SKB_CB(skb)->end_seq, tp->snd_una))
2114 if (tcp_trim_head(sk, skb, tp->snd_una - TCP_SKB_CB(skb)->seq))
2118 if (inet_csk(sk)->icsk_af_ops->rebuild_header(sk))
2119 return -EHOSTUNREACH; /* Routing failure or similar. */
2121 cur_mss = tcp_current_mss(sk);
2123 /* If receiver has shrunk his window, and skb is out of
2124 * new window, do not retransmit it. The exception is the
2125 * case, when window is shrunk to zero. In this case
2126 * our retransmit serves as a zero window probe.
2128 if (!before(TCP_SKB_CB(skb)->seq, tcp_wnd_end(tp)) &&
2129 TCP_SKB_CB(skb)->seq != tp->snd_una)
2132 if (skb->len > cur_mss) {
2133 if (tcp_fragment(sk, skb, cur_mss, cur_mss))
2134 return -ENOMEM; /* We'll try again later. */
2136 int oldpcount = tcp_skb_pcount(skb);
2138 if (unlikely(oldpcount > 1)) {
2139 tcp_init_tso_segs(sk, skb, cur_mss);
2140 tcp_adjust_pcount(sk, skb, oldpcount - tcp_skb_pcount(skb));
2144 tcp_retrans_try_collapse(sk, skb, cur_mss);
2146 /* Some Solaris stacks overoptimize and ignore the FIN on a
2147 * retransmit when old data is attached. So strip it off
2148 * since it is cheap to do so and saves bytes on the network.
2151 (TCP_SKB_CB(skb)->tcp_flags & TCPHDR_FIN) &&
2152 tp->snd_una == (TCP_SKB_CB(skb)->end_seq - 1)) {
2153 if (!pskb_trim(skb, 0)) {
2154 /* Reuse, even though it does some unnecessary work */
2155 tcp_init_nondata_skb(skb, TCP_SKB_CB(skb)->end_seq - 1,
2156 TCP_SKB_CB(skb)->tcp_flags);
2157 skb->ip_summed = CHECKSUM_NONE;
2161 /* Make a copy, if the first transmission SKB clone we made
2162 * is still in somebody's hands, else make a clone.
2164 TCP_SKB_CB(skb)->when = tcp_time_stamp;
2166 /* make sure skb->data is aligned on arches that require it */
2167 if (unlikely(NET_IP_ALIGN && ((unsigned long)skb->data & 3))) {
2168 struct sk_buff *nskb = __pskb_copy(skb, MAX_TCP_HEADER,
2170 err = nskb ? tcp_transmit_skb(sk, nskb, 0, GFP_ATOMIC) :
2173 err = tcp_transmit_skb(sk, skb, 1, GFP_ATOMIC);
2177 /* Update global TCP statistics. */
2178 TCP_INC_STATS(sock_net(sk), TCP_MIB_RETRANSSEGS);
2180 tp->total_retrans++;
2182 #if FASTRETRANS_DEBUG > 0
2183 if (TCP_SKB_CB(skb)->sacked & TCPCB_SACKED_RETRANS) {
2184 if (net_ratelimit())
2185 printk(KERN_DEBUG "retrans_out leaked.\n");
2188 if (!tp->retrans_out)
2189 tp->lost_retrans_low = tp->snd_nxt;
2190 TCP_SKB_CB(skb)->sacked |= TCPCB_RETRANS;
2191 tp->retrans_out += tcp_skb_pcount(skb);
2193 /* Save stamp of the first retransmit. */
2194 if (!tp->retrans_stamp)
2195 tp->retrans_stamp = TCP_SKB_CB(skb)->when;
2197 tp->undo_retrans += tcp_skb_pcount(skb);
2199 /* snd_nxt is stored to detect loss of retransmitted segment,
2200 * see tcp_input.c tcp_sacktag_write_queue().
2202 TCP_SKB_CB(skb)->ack_seq = tp->snd_nxt;
2207 /* Check if we forward retransmits are possible in the current
2208 * window/congestion state.
2210 static int tcp_can_forward_retransmit(struct sock *sk)
2212 const struct inet_connection_sock *icsk = inet_csk(sk);
2213 const struct tcp_sock *tp = tcp_sk(sk);
2215 /* Forward retransmissions are possible only during Recovery. */
2216 if (icsk->icsk_ca_state != TCP_CA_Recovery)
2219 /* No forward retransmissions in Reno are possible. */
2220 if (tcp_is_reno(tp))
2223 /* Yeah, we have to make difficult choice between forward transmission
2224 * and retransmission... Both ways have their merits...
2226 * For now we do not retransmit anything, while we have some new
2227 * segments to send. In the other cases, follow rule 3 for
2228 * NextSeg() specified in RFC3517.
2231 if (tcp_may_send_now(sk))
2237 /* This gets called after a retransmit timeout, and the initially
2238 * retransmitted data is acknowledged. It tries to continue
2239 * resending the rest of the retransmit queue, until either
2240 * we've sent it all or the congestion window limit is reached.
2241 * If doing SACK, the first ACK which comes back for a timeout
2242 * based retransmit packet might feed us FACK information again.
2243 * If so, we use it to avoid unnecessarily retransmissions.
2245 void tcp_xmit_retransmit_queue(struct sock *sk)
2247 const struct inet_connection_sock *icsk = inet_csk(sk);
2248 struct tcp_sock *tp = tcp_sk(sk);
2249 struct sk_buff *skb;
2250 struct sk_buff *hole = NULL;
2253 int fwd_rexmitting = 0;
2255 if (!tp->packets_out)
2259 tp->retransmit_high = tp->snd_una;
2261 if (tp->retransmit_skb_hint) {
2262 skb = tp->retransmit_skb_hint;
2263 last_lost = TCP_SKB_CB(skb)->end_seq;
2264 if (after(last_lost, tp->retransmit_high))
2265 last_lost = tp->retransmit_high;
2267 skb = tcp_write_queue_head(sk);
2268 last_lost = tp->snd_una;
2271 tcp_for_write_queue_from(skb, sk) {
2272 __u8 sacked = TCP_SKB_CB(skb)->sacked;
2274 if (skb == tcp_send_head(sk))
2276 /* we could do better than to assign each time */
2278 tp->retransmit_skb_hint = skb;
2280 /* Assume this retransmit will generate
2281 * only one packet for congestion window
2282 * calculation purposes. This works because
2283 * tcp_retransmit_skb() will chop up the
2284 * packet to be MSS sized and all the
2285 * packet counting works out.
2287 if (tcp_packets_in_flight(tp) >= tp->snd_cwnd)
2290 if (fwd_rexmitting) {
2292 if (!before(TCP_SKB_CB(skb)->seq, tcp_highest_sack_seq(tp)))
2294 mib_idx = LINUX_MIB_TCPFORWARDRETRANS;
2296 } else if (!before(TCP_SKB_CB(skb)->seq, tp->retransmit_high)) {
2297 tp->retransmit_high = last_lost;
2298 if (!tcp_can_forward_retransmit(sk))
2300 /* Backtrack if necessary to non-L'ed skb */
2308 } else if (!(sacked & TCPCB_LOST)) {
2309 if (hole == NULL && !(sacked & (TCPCB_SACKED_RETRANS|TCPCB_SACKED_ACKED)))
2314 last_lost = TCP_SKB_CB(skb)->end_seq;
2315 if (icsk->icsk_ca_state != TCP_CA_Loss)
2316 mib_idx = LINUX_MIB_TCPFASTRETRANS;
2318 mib_idx = LINUX_MIB_TCPSLOWSTARTRETRANS;
2321 if (sacked & (TCPCB_SACKED_ACKED|TCPCB_SACKED_RETRANS))
2324 if (tcp_retransmit_skb(sk, skb)) {
2325 NET_INC_STATS_BH(sock_net(sk), LINUX_MIB_TCPRETRANSFAIL);
2328 NET_INC_STATS_BH(sock_net(sk), mib_idx);
2330 if (inet_csk(sk)->icsk_ca_state == TCP_CA_Recovery)
2331 tp->prr_out += tcp_skb_pcount(skb);
2333 if (skb == tcp_write_queue_head(sk))
2334 inet_csk_reset_xmit_timer(sk, ICSK_TIME_RETRANS,
2335 inet_csk(sk)->icsk_rto,
2340 /* Send a fin. The caller locks the socket for us. This cannot be
2341 * allowed to fail queueing a FIN frame under any circumstances.
2343 void tcp_send_fin(struct sock *sk)
2345 struct tcp_sock *tp = tcp_sk(sk);
2346 struct sk_buff *skb = tcp_write_queue_tail(sk);
2349 /* Optimization, tack on the FIN if we have a queue of
2350 * unsent frames. But be careful about outgoing SACKS
2353 mss_now = tcp_current_mss(sk);
2355 if (tcp_send_head(sk) != NULL) {
2356 TCP_SKB_CB(skb)->tcp_flags |= TCPHDR_FIN;
2357 TCP_SKB_CB(skb)->end_seq++;
2360 /* Socket is locked, keep trying until memory is available. */
2362 skb = alloc_skb_fclone(MAX_TCP_HEADER,
2369 /* Reserve space for headers and prepare control bits. */
2370 skb_reserve(skb, MAX_TCP_HEADER);
2371 /* FIN eats a sequence byte, write_seq advanced by tcp_queue_skb(). */
2372 tcp_init_nondata_skb(skb, tp->write_seq,
2373 TCPHDR_ACK | TCPHDR_FIN);
2374 tcp_queue_skb(sk, skb);
2376 __tcp_push_pending_frames(sk, mss_now, TCP_NAGLE_OFF);
2379 /* We get here when a process closes a file descriptor (either due to
2380 * an explicit close() or as a byproduct of exit()'ing) and there
2381 * was unread data in the receive queue. This behavior is recommended
2382 * by RFC 2525, section 2.17. -DaveM
2384 void tcp_send_active_reset(struct sock *sk, gfp_t priority)
2386 struct sk_buff *skb;
2388 /* NOTE: No TCP options attached and we never retransmit this. */
2389 skb = alloc_skb(MAX_TCP_HEADER, priority);
2391 NET_INC_STATS(sock_net(sk), LINUX_MIB_TCPABORTFAILED);
2395 /* Reserve space for headers and prepare control bits. */
2396 skb_reserve(skb, MAX_TCP_HEADER);
2397 tcp_init_nondata_skb(skb, tcp_acceptable_seq(sk),
2398 TCPHDR_ACK | TCPHDR_RST);
2400 TCP_SKB_CB(skb)->when = tcp_time_stamp;
2401 if (tcp_transmit_skb(sk, skb, 0, priority))
2402 NET_INC_STATS(sock_net(sk), LINUX_MIB_TCPABORTFAILED);
2404 TCP_INC_STATS(sock_net(sk), TCP_MIB_OUTRSTS);
2407 /* Send a crossed SYN-ACK during socket establishment.
2408 * WARNING: This routine must only be called when we have already sent
2409 * a SYN packet that crossed the incoming SYN that caused this routine
2410 * to get called. If this assumption fails then the initial rcv_wnd
2411 * and rcv_wscale values will not be correct.
2413 int tcp_send_synack(struct sock *sk)
2415 struct sk_buff *skb;
2417 skb = tcp_write_queue_head(sk);
2418 if (skb == NULL || !(TCP_SKB_CB(skb)->tcp_flags & TCPHDR_SYN)) {
2419 printk(KERN_DEBUG "tcp_send_synack: wrong queue state\n");
2422 if (!(TCP_SKB_CB(skb)->tcp_flags & TCPHDR_ACK)) {
2423 if (skb_cloned(skb)) {
2424 struct sk_buff *nskb = skb_copy(skb, GFP_ATOMIC);
2427 tcp_unlink_write_queue(skb, sk);
2428 skb_header_release(nskb);
2429 __tcp_add_write_queue_head(sk, nskb);
2430 sk_wmem_free_skb(sk, skb);
2431 sk->sk_wmem_queued += nskb->truesize;
2432 sk_mem_charge(sk, nskb->truesize);
2436 TCP_SKB_CB(skb)->tcp_flags |= TCPHDR_ACK;
2437 TCP_ECN_send_synack(tcp_sk(sk), skb);
2439 TCP_SKB_CB(skb)->when = tcp_time_stamp;
2440 return tcp_transmit_skb(sk, skb, 1, GFP_ATOMIC);
2443 /* Prepare a SYN-ACK. */
2444 struct sk_buff *tcp_make_synack(struct sock *sk, struct dst_entry *dst,
2445 struct request_sock *req,
2446 struct request_values *rvp)
2448 struct tcp_out_options opts;
2449 struct tcp_extend_values *xvp = tcp_xv(rvp);
2450 struct inet_request_sock *ireq = inet_rsk(req);
2451 struct tcp_sock *tp = tcp_sk(sk);
2452 const struct tcp_cookie_values *cvp = tp->cookie_values;
2454 struct sk_buff *skb;
2455 struct tcp_md5sig_key *md5;
2456 int tcp_header_size;
2458 int s_data_desired = 0;
2460 if (cvp != NULL && cvp->s_data_constant && cvp->s_data_desired)
2461 s_data_desired = cvp->s_data_desired;
2462 skb = sock_wmalloc(sk, MAX_TCP_HEADER + 15 + s_data_desired, 1, GFP_ATOMIC);
2466 /* Reserve space for headers. */
2467 skb_reserve(skb, MAX_TCP_HEADER);
2469 skb_dst_set(skb, dst_clone(dst));
2471 mss = dst_metric_advmss(dst);
2472 if (tp->rx_opt.user_mss && tp->rx_opt.user_mss < mss)
2473 mss = tp->rx_opt.user_mss;
2475 if (req->rcv_wnd == 0) { /* ignored for retransmitted syns */
2477 /* Set this up on the first call only */
2478 req->window_clamp = tp->window_clamp ? : dst_metric(dst, RTAX_WINDOW);
2480 /* limit the window selection if the user enforce a smaller rx buffer */
2481 if (sk->sk_userlocks & SOCK_RCVBUF_LOCK &&
2482 (req->window_clamp > tcp_full_space(sk) || req->window_clamp == 0))
2483 req->window_clamp = tcp_full_space(sk);
2485 /* tcp_full_space because it is guaranteed to be the first packet */
2486 tcp_select_initial_window(tcp_full_space(sk),
2487 mss - (ireq->tstamp_ok ? TCPOLEN_TSTAMP_ALIGNED : 0),
2492 dst_metric(dst, RTAX_INITRWND));
2493 ireq->rcv_wscale = rcv_wscale;
2496 memset(&opts, 0, sizeof(opts));
2497 #ifdef CONFIG_SYN_COOKIES
2498 if (unlikely(req->cookie_ts))
2499 TCP_SKB_CB(skb)->when = cookie_init_timestamp(req);
2502 TCP_SKB_CB(skb)->when = tcp_time_stamp;
2503 tcp_header_size = tcp_synack_options(sk, req, mss,
2504 skb, &opts, &md5, xvp)
2507 skb_push(skb, tcp_header_size);
2508 skb_reset_transport_header(skb);
2511 memset(th, 0, sizeof(struct tcphdr));
2514 TCP_ECN_make_synack(req, th);
2515 th->source = ireq->loc_port;
2516 th->dest = ireq->rmt_port;
2517 /* Setting of flags are superfluous here for callers (and ECE is
2518 * not even correctly set)
2520 tcp_init_nondata_skb(skb, tcp_rsk(req)->snt_isn,
2521 TCPHDR_SYN | TCPHDR_ACK);
2523 if (OPTION_COOKIE_EXTENSION & opts.options) {
2524 if (s_data_desired) {
2525 u8 *buf = skb_put(skb, s_data_desired);
2527 /* copy data directly from the listening socket. */
2528 memcpy(buf, cvp->s_data_payload, s_data_desired);
2529 TCP_SKB_CB(skb)->end_seq += s_data_desired;
2532 if (opts.hash_size > 0) {
2533 __u32 workspace[SHA_WORKSPACE_WORDS];
2534 u32 *mess = &xvp->cookie_bakery[COOKIE_DIGEST_WORDS];
2535 u32 *tail = &mess[COOKIE_MESSAGE_WORDS-1];
2537 /* Secret recipe depends on the Timestamp, (future)
2538 * Sequence and Acknowledgment Numbers, Initiator
2539 * Cookie, and others handled by IP variant caller.
2541 *tail-- ^= opts.tsval;
2542 *tail-- ^= tcp_rsk(req)->rcv_isn + 1;
2543 *tail-- ^= TCP_SKB_CB(skb)->seq + 1;
2546 *tail-- ^= (((__force u32)th->dest << 16) | (__force u32)th->source);
2547 *tail-- ^= (u32)(unsigned long)cvp; /* per sockopt */
2549 sha_transform((__u32 *)&xvp->cookie_bakery[0],
2552 opts.hash_location =
2553 (__u8 *)&xvp->cookie_bakery[0];
2557 th->seq = htonl(TCP_SKB_CB(skb)->seq);
2558 th->ack_seq = htonl(tcp_rsk(req)->rcv_isn + 1);
2560 /* RFC1323: The window in SYN & SYN/ACK segments is never scaled. */
2561 th->window = htons(min(req->rcv_wnd, 65535U));
2562 tcp_options_write((__be32 *)(th + 1), tp, &opts);
2563 th->doff = (tcp_header_size >> 2);
2564 TCP_ADD_STATS(sock_net(sk), TCP_MIB_OUTSEGS, tcp_skb_pcount(skb));
2566 #ifdef CONFIG_TCP_MD5SIG
2567 /* Okay, we have all we need - do the md5 hash if needed */
2569 tcp_rsk(req)->af_specific->calc_md5_hash(opts.hash_location,
2570 md5, NULL, req, skb);
2576 EXPORT_SYMBOL(tcp_make_synack);
2578 /* Do all connect socket setups that can be done AF independent. */
2579 void tcp_connect_init(struct sock *sk)
2581 const struct dst_entry *dst = __sk_dst_get(sk);
2582 struct tcp_sock *tp = tcp_sk(sk);
2585 /* We'll fix this up when we get a response from the other end.
2586 * See tcp_input.c:tcp_rcv_state_process case TCP_SYN_SENT.
2588 tp->tcp_header_len = sizeof(struct tcphdr) +
2589 (sysctl_tcp_timestamps ? TCPOLEN_TSTAMP_ALIGNED : 0);
2591 #ifdef CONFIG_TCP_MD5SIG
2592 if (tp->af_specific->md5_lookup(sk, sk) != NULL)
2593 tp->tcp_header_len += TCPOLEN_MD5SIG_ALIGNED;
2596 /* If user gave his TCP_MAXSEG, record it to clamp */
2597 if (tp->rx_opt.user_mss)
2598 tp->rx_opt.mss_clamp = tp->rx_opt.user_mss;
2601 tcp_sync_mss(sk, dst_mtu(dst));
2603 if (!tp->window_clamp)
2604 tp->window_clamp = dst_metric(dst, RTAX_WINDOW);
2605 tp->advmss = dst_metric_advmss(dst);
2606 if (tp->rx_opt.user_mss && tp->rx_opt.user_mss < tp->advmss)
2607 tp->advmss = tp->rx_opt.user_mss;
2609 tcp_initialize_rcv_mss(sk);
2611 /* limit the window selection if the user enforce a smaller rx buffer */
2612 if (sk->sk_userlocks & SOCK_RCVBUF_LOCK &&
2613 (tp->window_clamp > tcp_full_space(sk) || tp->window_clamp == 0))
2614 tp->window_clamp = tcp_full_space(sk);
2616 tcp_select_initial_window(tcp_full_space(sk),
2617 tp->advmss - (tp->rx_opt.ts_recent_stamp ? tp->tcp_header_len - sizeof(struct tcphdr) : 0),
2620 sysctl_tcp_window_scaling,
2622 dst_metric(dst, RTAX_INITRWND));
2624 tp->rx_opt.rcv_wscale = rcv_wscale;
2625 tp->rcv_ssthresh = tp->rcv_wnd;
2628 sock_reset_flag(sk, SOCK_DONE);
2631 tp->snd_una = tp->write_seq;
2632 tp->snd_sml = tp->write_seq;
2633 tp->snd_up = tp->write_seq;
2634 tp->snd_nxt = tp->write_seq;
2636 if (likely(!tp->repair))
2638 tp->rcv_wup = tp->rcv_nxt;
2639 tp->copied_seq = tp->rcv_nxt;
2641 inet_csk(sk)->icsk_rto = TCP_TIMEOUT_INIT;
2642 inet_csk(sk)->icsk_retransmits = 0;
2643 tcp_clear_retrans(tp);
2646 /* Build a SYN and send it off. */
2647 int tcp_connect(struct sock *sk)
2649 struct tcp_sock *tp = tcp_sk(sk);
2650 struct sk_buff *buff;
2653 tcp_connect_init(sk);
2655 buff = alloc_skb_fclone(MAX_TCP_HEADER + 15, sk->sk_allocation);
2656 if (unlikely(buff == NULL))
2659 /* Reserve space for headers. */
2660 skb_reserve(buff, MAX_TCP_HEADER);
2662 tcp_init_nondata_skb(buff, tp->write_seq++, TCPHDR_SYN);
2663 TCP_ECN_send_syn(sk, buff);
2666 TCP_SKB_CB(buff)->when = tcp_time_stamp;
2667 tp->retrans_stamp = TCP_SKB_CB(buff)->when;
2668 skb_header_release(buff);
2669 __tcp_add_write_queue_tail(sk, buff);
2670 sk->sk_wmem_queued += buff->truesize;
2671 sk_mem_charge(sk, buff->truesize);
2672 tp->packets_out += tcp_skb_pcount(buff);
2673 err = tcp_transmit_skb(sk, buff, 1, sk->sk_allocation);
2674 if (err == -ECONNREFUSED)
2677 /* We change tp->snd_nxt after the tcp_transmit_skb() call
2678 * in order to make this packet get counted in tcpOutSegs.
2680 tp->snd_nxt = tp->write_seq;
2681 tp->pushed_seq = tp->write_seq;
2682 TCP_INC_STATS(sock_net(sk), TCP_MIB_ACTIVEOPENS);
2684 /* Timer for repeating the SYN until an answer. */
2685 inet_csk_reset_xmit_timer(sk, ICSK_TIME_RETRANS,
2686 inet_csk(sk)->icsk_rto, TCP_RTO_MAX);
2689 EXPORT_SYMBOL(tcp_connect);
2691 /* Send out a delayed ack, the caller does the policy checking
2692 * to see if we should even be here. See tcp_input.c:tcp_ack_snd_check()
2695 void tcp_send_delayed_ack(struct sock *sk)
2697 struct inet_connection_sock *icsk = inet_csk(sk);
2698 int ato = icsk->icsk_ack.ato;
2699 unsigned long timeout;
2701 if (ato > TCP_DELACK_MIN) {
2702 const struct tcp_sock *tp = tcp_sk(sk);
2703 int max_ato = HZ / 2;
2705 if (icsk->icsk_ack.pingpong ||
2706 (icsk->icsk_ack.pending & ICSK_ACK_PUSHED))
2707 max_ato = TCP_DELACK_MAX;
2709 /* Slow path, intersegment interval is "high". */
2711 /* If some rtt estimate is known, use it to bound delayed ack.
2712 * Do not use inet_csk(sk)->icsk_rto here, use results of rtt measurements
2716 int rtt = max(tp->srtt >> 3, TCP_DELACK_MIN);
2722 ato = min(ato, max_ato);
2725 /* Stay within the limit we were given */
2726 timeout = jiffies + ato;
2728 /* Use new timeout only if there wasn't a older one earlier. */
2729 if (icsk->icsk_ack.pending & ICSK_ACK_TIMER) {
2730 /* If delack timer was blocked or is about to expire,
2733 if (icsk->icsk_ack.blocked ||
2734 time_before_eq(icsk->icsk_ack.timeout, jiffies + (ato >> 2))) {
2739 if (!time_before(timeout, icsk->icsk_ack.timeout))
2740 timeout = icsk->icsk_ack.timeout;
2742 icsk->icsk_ack.pending |= ICSK_ACK_SCHED | ICSK_ACK_TIMER;
2743 icsk->icsk_ack.timeout = timeout;
2744 sk_reset_timer(sk, &icsk->icsk_delack_timer, timeout);
2747 /* This routine sends an ack and also updates the window. */
2748 void tcp_send_ack(struct sock *sk)
2750 struct sk_buff *buff;
2752 /* If we have been reset, we may not send again. */
2753 if (sk->sk_state == TCP_CLOSE)
2756 /* We are not putting this on the write queue, so
2757 * tcp_transmit_skb() will set the ownership to this
2760 buff = alloc_skb(MAX_TCP_HEADER, GFP_ATOMIC);
2762 inet_csk_schedule_ack(sk);
2763 inet_csk(sk)->icsk_ack.ato = TCP_ATO_MIN;
2764 inet_csk_reset_xmit_timer(sk, ICSK_TIME_DACK,
2765 TCP_DELACK_MAX, TCP_RTO_MAX);
2769 /* Reserve space for headers and prepare control bits. */
2770 skb_reserve(buff, MAX_TCP_HEADER);
2771 tcp_init_nondata_skb(buff, tcp_acceptable_seq(sk), TCPHDR_ACK);
2773 /* Send it off, this clears delayed acks for us. */
2774 TCP_SKB_CB(buff)->when = tcp_time_stamp;
2775 tcp_transmit_skb(sk, buff, 0, GFP_ATOMIC);
2778 /* This routine sends a packet with an out of date sequence
2779 * number. It assumes the other end will try to ack it.
2781 * Question: what should we make while urgent mode?
2782 * 4.4BSD forces sending single byte of data. We cannot send
2783 * out of window data, because we have SND.NXT==SND.MAX...
2785 * Current solution: to send TWO zero-length segments in urgent mode:
2786 * one is with SEG.SEQ=SND.UNA to deliver urgent pointer, another is
2787 * out-of-date with SND.UNA-1 to probe window.
2789 static int tcp_xmit_probe_skb(struct sock *sk, int urgent)
2791 struct tcp_sock *tp = tcp_sk(sk);
2792 struct sk_buff *skb;
2794 /* We don't queue it, tcp_transmit_skb() sets ownership. */
2795 skb = alloc_skb(MAX_TCP_HEADER, GFP_ATOMIC);
2799 /* Reserve space for headers and set control bits. */
2800 skb_reserve(skb, MAX_TCP_HEADER);
2801 /* Use a previous sequence. This should cause the other
2802 * end to send an ack. Don't queue or clone SKB, just
2805 tcp_init_nondata_skb(skb, tp->snd_una - !urgent, TCPHDR_ACK);
2806 TCP_SKB_CB(skb)->when = tcp_time_stamp;
2807 return tcp_transmit_skb(sk, skb, 0, GFP_ATOMIC);
2810 void tcp_send_window_probe(struct sock *sk)
2812 if (sk->sk_state == TCP_ESTABLISHED) {
2813 tcp_sk(sk)->snd_wl1 = tcp_sk(sk)->rcv_nxt - 1;
2814 tcp_sk(sk)->snd_nxt = tcp_sk(sk)->write_seq;
2815 tcp_xmit_probe_skb(sk, 0);
2819 /* Initiate keepalive or window probe from timer. */
2820 int tcp_write_wakeup(struct sock *sk)
2822 struct tcp_sock *tp = tcp_sk(sk);
2823 struct sk_buff *skb;
2825 if (sk->sk_state == TCP_CLOSE)
2828 if ((skb = tcp_send_head(sk)) != NULL &&
2829 before(TCP_SKB_CB(skb)->seq, tcp_wnd_end(tp))) {
2831 unsigned int mss = tcp_current_mss(sk);
2832 unsigned int seg_size = tcp_wnd_end(tp) - TCP_SKB_CB(skb)->seq;
2834 if (before(tp->pushed_seq, TCP_SKB_CB(skb)->end_seq))
2835 tp->pushed_seq = TCP_SKB_CB(skb)->end_seq;
2837 /* We are probing the opening of a window
2838 * but the window size is != 0
2839 * must have been a result SWS avoidance ( sender )
2841 if (seg_size < TCP_SKB_CB(skb)->end_seq - TCP_SKB_CB(skb)->seq ||
2843 seg_size = min(seg_size, mss);
2844 TCP_SKB_CB(skb)->tcp_flags |= TCPHDR_PSH;
2845 if (tcp_fragment(sk, skb, seg_size, mss))
2847 } else if (!tcp_skb_pcount(skb))
2848 tcp_set_skb_tso_segs(sk, skb, mss);
2850 TCP_SKB_CB(skb)->tcp_flags |= TCPHDR_PSH;
2851 TCP_SKB_CB(skb)->when = tcp_time_stamp;
2852 err = tcp_transmit_skb(sk, skb, 1, GFP_ATOMIC);
2854 tcp_event_new_data_sent(sk, skb);
2857 if (between(tp->snd_up, tp->snd_una + 1, tp->snd_una + 0xFFFF))
2858 tcp_xmit_probe_skb(sk, 1);
2859 return tcp_xmit_probe_skb(sk, 0);
2863 /* A window probe timeout has occurred. If window is not closed send
2864 * a partial packet else a zero probe.
2866 void tcp_send_probe0(struct sock *sk)
2868 struct inet_connection_sock *icsk = inet_csk(sk);
2869 struct tcp_sock *tp = tcp_sk(sk);
2872 err = tcp_write_wakeup(sk);
2874 if (tp->packets_out || !tcp_send_head(sk)) {
2875 /* Cancel probe timer, if it is not required. */
2876 icsk->icsk_probes_out = 0;
2877 icsk->icsk_backoff = 0;
2882 if (icsk->icsk_backoff < sysctl_tcp_retries2)
2883 icsk->icsk_backoff++;
2884 icsk->icsk_probes_out++;
2885 inet_csk_reset_xmit_timer(sk, ICSK_TIME_PROBE0,
2886 min(icsk->icsk_rto << icsk->icsk_backoff, TCP_RTO_MAX),
2889 /* If packet was not sent due to local congestion,
2890 * do not backoff and do not remember icsk_probes_out.
2891 * Let local senders to fight for local resources.
2893 * Use accumulated backoff yet.
2895 if (!icsk->icsk_probes_out)
2896 icsk->icsk_probes_out = 1;
2897 inet_csk_reset_xmit_timer(sk, ICSK_TIME_PROBE0,
2898 min(icsk->icsk_rto << icsk->icsk_backoff,
2899 TCP_RESOURCE_PROBE_INTERVAL),